Chemical linkers and conjugates thereof

ABSTRACT

The present disclosure provides drug-ligand conjugates that are potent cytotoxins, wherein the drug is linked to the ligand through either a peptidyl, hydrazine, or disulfide linker. The disclosure is also directed to compositions containing the drug-ligand conjugates, and to methods of treatment using them.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.11/134,826, filed May 19, 2005, which claims the benefit under 35 USC119(e) of U.S. Provisional Patent Application Ser. Nos. 60/572,667,filed on May 19, 2004, and 60/661,174, filed on Mar. 9, 2005, which areherein incorporated by reference.

FIELD OF THE INVENTION

The present invention provides linkers that attach to a drug and aligand and are cleaved in vivo. The linkers are of use in formingprodrugs and conjugates of the cytotoxins of the invention as well asother diagnostic and therapeutic moieties.

BACKGROUND OF THE INVENTION

Many therapeutic agents, particularly those that are especiallyeffective in cancer chemotherapy, often exhibit acute toxicity in vivo,especially bone marrow and mucosal toxicity, as well as chronic cardiacand neurological toxicity. Such high toxicity can limit theirapplications. Development of more and safer specific therapeutic agents,particularly antitumor agents, is desirable for greater effectivenessagainst tumor cells and a decrease in the number and severity of theside effects of these products (toxicity, destruction of non-tumorcells, etc.). Another difficulty with some existing therapeutic agentsis their less than optimal stability in plasma. Addition of functionalgroups to stabilize these compounds resulted in a significant loweringof the activity. Accordingly, it is desirable to identify ways tostabilize compounds while maintaining acceptable therapeutic activitylevels.

The search for more selective cytotoxic agents has been extremely activefor many decades, the dose limiting toxicity (i.e. the undesirableactivity of the cytotoxins on normal tissues) being one of the majorcauses of failures in cancer therapy. For example, CC-1065 and theduocarmycins are known to be extremely potent cytotoxins.

CC-1065 was first isolated from Streptomyces zelensis in 1981 by theUpjohn Company (Hanka et al., J. Antibiot. 31: 1211 (1978); Martin etal., J. Antibiot. 33: 902 (1980); Martin et al., J. Antibiot. 34: 1119(1981)) and was found to have potent antitumor and antimicrobialactivity both in vitro and in experimental animals (Li et al., CancerRes. 42: 999 (1982)). CC-1065 binds to double-stranded B-DNA within theminor groove (Swenson et al., Cancer Res. 42: 2821 (1982)) with thesequence preference of 5′-d(A/GNTTA)-3′ and 5′-d(AAAAA)-3′ and alkylatesthe N3 position of the 3′-adenine by its CPI left-hand unit present inthe molecule (Hurley et al., Science 226: 843 (1984)). Despite itspotent and broad antitumor activity, CC-1065 cannot be used in humansbecause it causes delayed death in experimental animals.

Many analogues and derivatives of CC-1065 and the duocarmycins are knownin the art. The research into the structure, synthesis and properties ofmany of the compounds has been reviewed. See, for example, Boger et al.,Angew. Chem. Int. Ed. Engl. 35: 1438 (1996); and Boger et al., Chem.Rev. 97: 787 (1997).

A group at Kyowa Hakko Kogya Co., Ltd. has prepared a number of CC-1065derivatives. See, for example, U.S. Pat. Nos. 5,101,038; 5,641,780;5,187,186; 5,070,092; 5,703,080; 5,070,092; 5,641,780; 5,101,038; and5,084,468; and published PCT application, WO 96/10405 and publishedEuropean application 0 537 575 A1.

The Upjohn Company (Pharmacia Upjohn) has also been active in preparingderivatives of CC-1065. See, for example, U.S. Pat. Nos. 5,739,350;4,978,757, 5,332,837 and 4,912,227.

Research has also focused on the development of new therapeutic agentswhich are in the form of prodrugs, compounds that are capable of beingconverted to drugs (active therapeutic compounds) in vivo by certainchemical or enzymatic modifications of their structure. For purposes ofreducing toxicity, this conversion is preferably confined to the site ofaction or target tissue rather than the circulatory system or non-targettissue. However, even prodrugs are problematic as many are characterizedby a low stability in blood and serum, due to the presence of enzymesthat degrade or activate the prodrugs before the prodrugs reach thedesired sites within the patient's body.

Bristol-Myers Squibb has described particular lysosomal enzyme-cleavableantitumor drug conjugates. See, for example, U.S. Pat. No. 6,214,345.This patent provides an aminobenzyl oxycarbonyl.

Seattle Genetics has published applications U.S. Pat. Appl. 2003/0096743and U.S. Pat. Appl. 2003/0130189, which describe p-aminobenzylethers indrug delivery agents. The linkers described in these applications arelimited to aminobenzyl ether compositions.

Other groups have also described linkers. See for example de Groot etal., J. Med. Chem. 42, 5277 (1999); de Groot et al. J. Org. Chem. 43,3093 (2000); de Groot et al., J. Med. Chem. 66, 8815, (2001); WO02/083180; Carl et al., J. Med. Chem. Lett. 24, 479, (1981); Dubowchiket al., Bioorg & Med. Chem. Lett. 8, 3347 (1998). These linkers includeaminobenzyl ether spacer, elongated electronic cascade and cyclizationspacer systems, cyclisation eliminations spacers, such as w-aminoaminocarbonyls, and a p aminobenzyl oxycarbonyl linker.

Stability of cytotoxin drugs, including in vivo stability, is still animportant issue that needs to be addressed. In addition, the toxicity ofmany compounds makes them less useful, so compositions that will reducedrug toxicity, such as the formation of a cleaveable prodrug, areneeded. Therefore, in spite of the advances in the art, there continuesto be a need for the development of improved therapeutic agents for thetreatment of mammals, and humans in particular, more specificallycytotoxins that exhibit high specificity of action, reduced toxicity,and improved stability in blood relative to known compounds of similarstructure. The instant invention addresses those needs.

SUMMARY OF THE INVENTION

The present invention relates to drug-ligand conjugates where the drugand ligand are linked through a peptidyl, hydrazine, or disulfidelinker. These conjugates are potent cytotoxins that can be selectivelydelivered to a site of action of interest in an active form and thencleaved to release the active drug. The new linker arms of the inventioncan be cleaved from the cytotoxic drugs by, for example, enzymatic orreductive means in vivo, releasing an active drug moiety from theprodrug derivative. Furthermore, the invention includes conjugatesbetween the linker arms and the cytotoxins of the invention, andconjugates between the linker arms, the cytotoxin and a targeting agent,such as an antibody or a peptide.

The invention also relates to groups useful for stabilizing therapeuticagents and markers. The stabilizing groups are selected, for example, tolimit clearance and metabolism of the therapeutic agent or marker byenzymes that may be present in blood or non-target tissue. Thestabilizing groups can serve to block degradation of the agent or markerand may also act in providing other physical characteristics of theagent or marker, for example to increase the solubility of the compoundor to decrease the aggregation properties of the compound. Thestabilizing group may also improve the agent or marker's stabilityduring storage in either a formulated or non-formulated form.

In a first aspect, the invention provides a cytotoxic drug-ligandcompound having a structure according to any of Formulas 1-3:

wherein the symbol D is a drug moiety having pendant to the backbonethereof a chemically reactive functional group, said functional groupselected from the group consisting of a primary or secondary amine,hydroxyl, sulfhydryl, carboxyl, aldehyde, and a ketone.

The symbol L¹ represents a self-immolative spacer where m is an integerof 0, 1, 2, 3, 4, 5, or 6.

The symbol X⁴ represents a member selected from the group consisting ofprotected reactive functional groups, unprotected reactive functionalgroups, detectable labels, and targeting agents.

The symbol L⁴ represents a linker member, and p is 0 or 1. L⁴ is amoiety that imparts increased solubility or decreased aggregationproperties to the conjugates. Examples of L⁴ moieties includesubstituted alkyl, unsubstituted alkyl, substituted aryl, unsubstitutedaryl, substituted heteroalkyl, or unsubstituted heteroalkyl, any ofwhich may be straight, branched, or cyclic, a positively or negativelycharged amino acid polymer, such as polylysine or polyargenine, or otherpolymers such as polyethylene glycol.

The symbols F, H, and J represent linkers, as described further herein.

In one embodiment, the invention pertains to peptide linker conjugate ofthe structure:

wherein

-   -   D is a drug moiety having pendant to the backbone thereof a        chemically reactive functional group, said functional group        selected from the group consisting of a primary or secondary        amine, hydroxyl, thiol, carboxyl, aldehyde, and a ketone;    -   L¹ is a self-immolative linker;    -   m is an integer 0, 1, 2, 3, 4, 5, or 6;    -   F is a linker comprising the structure:

wherein

-   -   AA¹ is one or more members independently selected from the group        consisting of natural amino acids and unnatural α-amino acids;    -   c is an integer from 1 to 20;    -   L² is a self-immolative linker;    -   L³ is a spacer group comprising a primary or secondary amine or        a carboxyl functional group; wherein if L³ is present, m is 0        and either the amine of L³ forms an amide bond with a pendant        carboxyl functional group of D or the carboxyl of L³ forms an        amide bond with a pendant amine functional group of D;    -   o is 0 or 1;    -   L⁴ is a linker member, wherein L⁴ does not comprise a carboxylic        acyl group directly attached to the N-terminus of (AA¹)_(c);    -   p is 0 or 1; and    -   X⁴ is a member selected from the group consisting of protected        reactive functional groups, unprotected reactive functional        groups, detectable labels, and targeting agents.

In one embodiment, the peptide linker conjugate comprises the followingstructure:

In another embodiment, the peptide linker conjugate comprises thefollowing structure:

In a preferred embodiment, L³ comprises an aromatic group. For example,L³ can comprise a benzoic acid group, an aniline group, or an indolegroup. Non-limiting examples of -L³-NH— include structures selected fromthe following group:

wherein Z is a member selected from O, S and NR²³, and

wherein R²³ is a member selected from H, substituted or unsubstitutedalkyl, substituted or unsubstituted heteroalkyl, and acyl.

In preferred embodiments of the peptide linker, (AA¹)_(c) is a peptidesequence cleavable by a protease expressed in tumor tissue. A preferredprotease is a lysosomal protease. In preferred embodiments, c is aninteger from 2 to 6, or c is 2, 3 or 4. In certain embodiments, theamino acid in (AA¹)_(c) located closest to the drug moiety is selectedfrom the group consisting of: Ala, Asn, Asp, Cit, Cys, Gln, Glu, Gly,Ile, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Tyr, and Val. In preferredembodiments, (AA¹)_(c) is a peptide sequence selected from the groupconsisting of Val-Cit, Val-Lys, Phe-Lys, Lys-Lys, Ala-Lys, Phe-Cit,Leu-Cit, Ile-Cit, Trp, Cit, Phe-Ala, Phe-N⁹-tosyl-Arg, Phe-N⁹-nitro-Arg,Phe-Phe-Lys, D-Phe-Phe-Lys, Gly-Phe-Lys, Leu-Ala-Leu, Ile-Ala-Leu,Val-Ala-Val, Ala-Leu-Ala-Leu (SEQ ID NO: 1), β-Ala-Leu-Ala-Leu (SEQ IDNO: 2) and Gly-Phe-Leu-Gly (SEQ ID NO: 3). In particularly preferredembodiments, (AA¹)_(c) is Val-Cit or Val-Lys.

In some preferred embodiments, the peptide linker, F, comprises thestructure:

-   -   wherein        -   R²⁴ is selected from the group consisting of H, substituted            alkyl, unsubstituted alkyl, substituted heteroalkyl, and            unsubstituted heteroalkyl;        -   Each K is a member independently selected from the group            consisting of substituted alkyl, unsubstituted alkyl,            substituted heteroalkyl, unsubstituted heteroalkyl,            substituted aryl, unsubstituted aryl, substituted            heteroaryl, unsubstituted heteroaryl, substituted            heterocycloalkyl, unsubstituted heterocycloalkyl, halogen,            NO₂, NR²¹R²², NR²¹COR²², OCONR²¹R²², and OROR²¹, and OR²¹    -   wherein        -   R²¹ and R²² are independently selected from the group            consisting of H, substituted alkyl, unsubstituted alkyl,            substituted heteroalkyl, unsubstituted heteroalkyl,            substituted aryl, unsubstituted aryl, substituted            heteroaryl, unsubstituted heteroaryl, substituted            heterocycloalkyl, unsubstituted heterocycloalkyl; and        -   a is an integer of 0, 1, 2, 3, or 4.

In other preferred embodiments, —F-(L¹)_(m)- comprises the structure:

-   -   wherein        -   each R²⁴ is a member independently selected from the group            consisting of H, substituted alkyl, unsubstituted alkyl,            substituted heteroalkyl, and unsubstituted heteroalkyl.

In another aspect, the invention pertains to hydrazine linker conjugatesof the structure:X⁴-(L⁴)_(p)-H-(L¹)_(m)-D

wherein

-   -   D is a drug moiety having pendant to the backbone thereof a        chemically reactive functional group, said function group        selected from the group consisting of a primary or secondary        amine, hydroxyl, thiol, carboxyl, aldehyde, and a ketone;    -   L¹ is a self-immolative linker;    -   m is an integer selected from 0, 1, 2, 3, 4, 5, or 6;    -   X⁴ is a member selected from the group consisting of protected        reactive functional groups, unprotected reactive functional        groups, detectable labels, and targeting agents;    -   L⁴ is a linker member;    -   p is 0 or 1;    -   H is a linker comprising the structure:

wherein

-   -   n₁ is an integer from 1-10;    -   n₂ is 0, 1, or 2;    -   each R²⁴ is a member independently selected from the group        consisting of H, substituted alkyl, unsubstituted alkyl,        substituted heteroalkyl, and unsubstituted heteroalkyl; and    -   I is either a bond or:

wherein n₃ is 0 or 1 with the proviso that when n₃ is 0, n₂ is not 0;and

n₄ is 1, 2, or 3,

wherein when I is a bond, n₁ is 3 and n₂ is 1, D can not be

where R is Me or CH₂—CH₂—NMe₂.

In some preferred embodiments, the substitution on the phenyl ring is apara substitution. In some preferred embodiments, n₁ is 2, 3, or 4 or n₁is 3 or n₂ is 1.

In certain embodiments, I is a bond. In other embodiments, n₃ is 0 andn₄ is 2.

In various aspects, the invention provides hydrazine linkers, H, thatcan form a 6-membered self immolative linker upon cleavage, or two5-membered self immolative linkers upon cleavage, or a single 5-memberedself immolative linker upon cleavage, or a single 7-membered selfimmolative linker upon cleavage, or a 5-membered self immolative linkerand a 6-membered self immolative linker upon cleavage.

In a preferred embodiment, H comprises a geminal dimethyl substitution.

In a preferred embodiment, H comprises the structure:

Preferably, n₁ is 2, 3, or 4, more preferably n₁ is 3. Preferably, eachR₂₄ is independently selected from CH₃ and H. In certain preferredembodiments, each R₂₄ is H.

In another preferred embodiment, H comprises the structure:

Preferably, n₁ is 3. Preferably, each R₂₄ is independently selected fromCH₃ and H.

In yet other preferred embodiments, H comprises the structure:

Preferably, each R²⁴ independently an H or a substituted orunsubstituted alkyl.

In another aspect, the invention pertains to hydrazine linker conjugatesof the structure:X⁴-(L⁴)_(p)H-(L¹)_(m)-D

-   -   wherein        -   D is a drug moiety having pendant to the backbone thereof a            chemically reactive functional group, said function group            selected from the group consisting of a primary or secondary            amine, hydroxyl, thiol, carboxyl, aldehyde, and a ketone;        -   L¹ is a self-immolative linker;        -   m is an integer selected from 0, 1, 2, 3, 4, 5, or 6;        -   X⁴ is a member selected from the group consisting of            protected reactive functional groups, unprotected reactive            functional groups, detectable labels, and targeting agents;        -   L⁴ is a linker member;        -   p is 0 or 1; and        -   H comprises the structure:

-   -   -   where q is 0, 1, 2, 3, 4, 5, or 6; and        -   each R²⁴ is a member independently selected from the group            consisting of H, substituted alkyl, unsubstituted alkyl,            substituted heteroalkyl, and unsubstituted heteroalkyl.

In yet another aspect, the invention pertains to disulfide linkerconjugates of the structure:

-   -   wherein        -   D is a drug moiety having pendant to the backbone thereof a            chemically reactive functional group, said function group            selected from the group consisting of a primary or secondary            amine, hydroxyl, thiol, carboxyl, aldehyde, and a ketone;        -   L¹ is a self-immolative linker;        -   m is an integer selected from 0, 1, 2, 3, 4, 5, or 6;        -   X⁴ is a member selected from the group consisting of            protected reactive functional groups, unprotected reactive            functional groups, detectable labels, and targeting agents;        -   L⁴ is a linker member;        -   P is 0 or 1;        -   J is a linker comprising the structure:

-   -   wherein        -   each R²⁴ is a member independently selected from the group            consisting of H, substituted alkyl, unsubstituted alkyl,            substituted heteroalkyl, and unsubstituted heteroalkyl;        -   each K is a member independently selected from the group            consisting of H, substituted alkyl, unsubstituted alkyl,            substituted heteroalkyl, unsubstituted heteroalkyl,            substituted aryl, unsubstituted aryl, substituted            heteroaryl, unsubstituted heteroaryl, substituted            heterocycloalkyl, unsubstituted heterocycloalkyl, halogen,            NO₂, NR²¹R²², NR²¹COR²², OCONR²¹R²², OCOR²¹, and OR²¹    -   wherein        -   R²¹ and R²² are independently selected from the group            consisting of H, substituted alkyl, unsubstituted alkyl,            substituted heteroalkyl, unsubstituted heteroalkyl,            substituted aryl, unsubstituted aryl, substituted            heteroaryl, unsubstituted heteroaryl, substituted            heterocycloalkyl and unsubstituted heterocycloalkyl;        -   a is an integer of 0, 1, 2, 3, or 4; and        -   d is an integer of 0, 1, 2, 3, 4, 5, or 6.

In various embodiments, J can comprise one of the following structures:

-   -   wherein d is 1 or 2;

In all of the foregoing linker conjugates, D preferably is a cytotoxicdrug. In preferred embodiments, D has a chemically reactive functiongroup selected from the group consisting of a primary or secondaryamine, hydroxyl, sulfhydryl and carboxyl. Non-limiting examples ofpreferred drugs, D, include duocarmycins and duocarmycin analogs andderivatives, CC-1065, CBI-based duocarmycin analogues, MCBI-basedduocarmycin analogues, CCBI-based duocarmycin analogues, doxorubicin,doxorubicin conjugates, morpholino-doxorubicin,cyanomorpholino-doxorubicin, dolastatins, dolestatin-10, combretastatin,calicheamicin, maytansine, maytansine analogues, DM-1, auristatin E,auristatin EB (AEB), auristatin EFP (AEFP), monomethyl auristatin E(MMAE), 5-benzoylvaleric acid-AE ester (AEVB), tubulysins, disorazole,epothilones, Paclitaxel, docetaxel, SN-38, Topotecan, rhizoxin,echinomycin, colchicine, vinblastin, vindesine, estramustine, cemadotin,eleutherobin, methotrexate, methopterin, dichloromethotrexate,5-fluorouracil, 6-mercaptopurine, cytosine arabinoside, melphalan,leurosine, leurosideine, actinomycin, daunorubicin, daunorubicinconjugates, mitomycin C, mitomycin A, caminomycin, aminopterin,tallysomycin, podophyllotoxin, podophyllotoxin derivatives, etoposide,etoposide phosphate, vincristine, taxol, taxotere retinoic acid, butyricacid, N⁸-acetyl spermidine and camptothecin.

In a preferred embodiment, D is a duocarmycin analog or derivative thatcomprises a structure:

-   -   wherein the ring system A is a member selected from substituted        or unsubstituted aryl, substituted or unsubstituted heteroaryl        and substituted or unsubstituted heterocycloalkyl groups;    -   E and G are members independently selected from H, substituted        or unsubstituted alkyl, substituted or unsubstituted        heteroalkyl, a heteroatom, a single bond, or E and G are joined        to form a ring system selected from substituted or unsubstituted        aryl, substituted or unsubstituted heteroaryl and substituted or        unsubstituted heterocycloalkyl;    -   X is a member selected from O, S and NR²³;    -   R²³ is a member selected from H, substituted or unsubstituted        alkyl, substituted or unsubstituted heteroalkyl, and acyl;    -   R³ is a member selected from the group consisting of (═O), SR¹¹,        NHR¹¹ and OR¹¹,

wherein

-   -   R¹¹ is a member selected from the group consisting of H,        substituted alkyl, unsubstituted alkyl, substituted heteroalkyl,        unsubstituted heteroalkyl, diphosphates, triphosphates, acyl,        C(O)R¹²R¹³, C(O)OR¹², C(O)NR¹²R¹³, P(O)(OR¹²)₂, C(O)CHR¹²R¹³,        SR¹² and SiR¹²R¹³R¹⁴,

in which

-   -   R¹², R¹³ and R¹⁴ are members independently selected from H,        substituted or unsubstituted alkyl, substituted or unsubstituted        heteroalkyl and substituted or unsubstituted aryl, wherein R¹²        and R¹³ together with the nitrogen or carbon atom to which they        are attached are optionally joined to form a substituted or        unsubstituted heterocycloalkyl ring system having from 4 to 6        members, optionally containing two or more heteroatoms;    -   R⁴, R⁴′, R⁵ and R⁵′ are members independently selected from the        group consisting of H, substituted alkyl, unsubstituted alkyl,        substituted aryl, unsubstituted aryl, substituted heteroaryl,        unsubstituted heteroaryl, substituted heterocycloalkyl,        unsubstituted heterocycloalkyl, halogen, NO₂, NR¹⁵R¹⁶, NC(O)R¹⁵,        OC(O)NR¹⁵R¹⁶, OC(O)OR¹⁵, C(O)R¹⁵, SR¹⁵, OR¹⁵, CR¹⁵═NR¹⁶, and        O(CH₂)_(n)N(CH₃)₂

wherein

-   -   n is an integer from 1 to 20;    -   R¹⁵ and R¹⁶ are independently selected from H, substituted or        unsubstituted alkyl, substituted or unsubstituted heteroalkyl,        substituted or unsubstituted aryl, substituted or unsubstituted        heteroaryl, substituted or unsubstituted heterocycloalkyl, and        substituted or unsubstituted peptidyl, wherein R¹⁵ and R¹⁶        together with the nitrogen atom to which they are attached are        optionally joined to form a substituted or unsubstituted        heterocycloalkyl ring system having from 4 to 6 members,        optionally containing two or more heteroatoms;    -   R⁶ is a single bond which is either present or absent and when        present R⁶ and R⁷ are joined to form a cyclopropyl ring; and    -   R⁷ is CH₂—X¹ or CH₂— joined in said cyclopropyl ring with R⁶,        wherein    -   X¹ is a leaving group,    -   wherein at least one of R¹¹, R¹², R¹³, R¹⁵ or R¹⁶ links said        drug to L¹, if present, or to F, H, or J.

In a preferred embodiment, D has the structure:

-   -   wherein        -   Z is a member selected from O, S and NR²³    -   wherein        -   R²³ is a member selected from H, substituted or            unsubstituted alkyl, substituted or unsubstituted            heteroalkyl, and acyl;        -   R¹ is H, substituted or unsubstituted lower alkyl, C(O)R⁸,            or CO₂R⁸, wherein R⁸ is a member selected from group            consisting of substituted alkyl, unsubstituted alkyl,            NR⁹R¹⁰, NR⁹NHR¹⁰, and OR⁹    -   in which        -   R⁹ and R¹⁰ are members independently selected from H,            substituted or unsubstituted alkyl and substituted or            unsubstituted heteroalkyl; and        -   R² is H, substituted alkyl or unsubstituted lower alkyl;        -   wherein at least one of R¹¹, R¹², R¹³, R¹⁵ or R¹⁶ links said            drug to L¹, if present, or to F, H, or J.

In a preferred embodiment of the above, R² is an unsubstituted loweralkyl.

In another preferred embodiment, D has the structure:

-   -   wherein    -   Z is a member selected from O, S and NR²³

wherein

-   -   R²³ is a member selected from H, substituted or unsubstituted        alkyl, substituted or unsubstituted heteroalkyl, and acyl;

R¹ is H, substituted or unsubstituted lower alkyl, C(O)R⁸, or CO₂R⁸,wherein R⁸ is a member selected from NR⁹R¹⁰ and OR⁹,

in which

-   -   R⁹ and R¹⁰ are members independently selected from H,        substituted or unsubstituted alkyl and substituted or        unsubstituted heteroalkyl;    -   R¹′ is H, substituted or unsubstituted lower alkyl, or C(O)R⁸,        wherein R⁸ is a member selected from NR⁹R¹⁰ and OR⁹,

in which

-   -   R⁹ and R¹⁰ are members independently selected from H,        substituted or unsubstituted alkyl and substituted or        unsubstituted heteroalkyl;    -   R² is H, or substituted or unsubstituted lower alkyl or        unsubstituted heteroalkyl or cyano or alkoxy; and    -   R²′ is H, or substituted or unsubstituted lower alkyl or        unsubstituted heteroalkyl,    -   wherein at least one of R¹¹, R¹², R¹³, R¹⁵ or R¹⁶ links said        drug to L¹, if present, or to F, H, or J.

In all of the foregoing linker conjugate structures, L⁴ preferablycomprises a non-cyclic moiety. L⁴ preferably increases solubility of thecompound as compared to the compound lacking L⁴ and/or L⁴ decreasesaggregation of the compound as compared to the compound lacking L⁴. In apreferred embodiment, L⁴ comprises a polyethylene glycol moiety. Thepolyethylene glycol moiety can contain, for example, 3-12 repeat units,or 2-6 repeat units or, more preferably, 4 repeat units.

In yet another aspect, the invention provides a cytotoxic drug-ligandcompound having a structure according to the following formula:

wherein the symbol L¹ represents a self-immolative spacer where m is aninteger of 0, 1, 2, 3, 4, 5, or 6.

The symbol X⁴ represents a member selected from the group consisting ofprotected reactive functional groups, unprotected reactive functionalgroups, detectable labels, and targeting agents.

The symbol L⁴ represents a linker member, and p is 0 or 1. L⁴ is amoiety that imparts increased solubility or decreased aggregationproperties to the conjugates. Examples of L⁴ moieties includesubstituted alkyl, unsubstituted alkyl, substituted aryl, unsubstitutedaryl, substituted heteroalkyl, or unsubstituted heteroalkyl, any ofwhich may be straight, branched, or cyclic, a positively or negativelycharged amino acid polymer, such as polylysine or polyargenine, or otherpolymers such as polyethylene glycol.

The symbol Q represent any cleavable linker including, but not limitedto, any of the peptidyl, hydrozone, and disulfide linkers describedherein. Cleavable linkers include those that can be selectively cleavedby a chemical or biological process and upon cleavage separate the drug,D¹, from X⁴.

The symbol D¹ represents a drug having the following formula:

-   -   wherein X and Z are members independently selected from O, S and        NR²³;    -   R²³ is a member selected from H, substituted or unsubstituted        alkyl, substituted or unsubstituted heteroalkyl, and acyl;    -   R¹ is H, substituted or unsubstituted lower alkyl, C(O)R⁸, or        CO₂R⁸,    -   R¹′ is H, substituted or unsubstituted lower alkyl, or C(O)R⁸,    -   wherein R⁸ is a member selected from NR⁹R¹⁰ and OR⁹ and R⁹ and        R¹⁰ are members independently selected from H, substituted or        unsubstituted alkyl and substituted or unsubstituted        heteroalkyl;    -   R² is H, or substituted or unsubstituted lower alkyl or        unsubstituted heteroalkyl or cyano or alkoxy;    -   R²′ is H, or substituted or unsubstituted lower alkyl or        unsubstituted heteroalkyl,    -   R³ is a member selected from the group consisting of SR¹¹, NHR¹¹        and OR¹¹, wherein R¹¹ is a member selected from the group        consisting of H, substituted alkyl, unsubstituted alkyl,        substituted heteroalkyl, unsubstituted heteroalkyl,        diphosphates, triphosphates, acyl, C(O)R¹²R¹³, C(O)OR¹²,        C(O)NR¹²R¹³, P(O)(OR¹²)₂, C(O)CHR¹²R¹³, SR¹² and SiR¹²R¹³R¹⁴, in        which R¹², R¹³, and R¹⁴ are members independently selected from        H, substituted or unsubstituted alkyl, substituted or        unsubstituted heteroalkyl and substituted or unsubstituted aryl,        wherein R¹² and R¹³ together with the nitrogen or carbon atom to        which they are attached are optionally joined to form a        substituted or unsubstituted heterocycloalkyl ring system having        from 4 to 6 members, optionally containing two or more        heteroatoms;    -   wherein at least one of R¹¹, R¹², and R¹³ links said drug to L¹,        if present, or to Q,    -   R⁶ is a single bond which is either present or absent and when        present R⁶ and R⁷ are joined to form a cyclopropyl ring; and    -   R⁷ is CH₂—X¹ or CH₂— joined in said cyclopropyl ring with R⁶,        wherein    -   X¹ is a leaving group,    -   R⁴, R⁴′, R⁵ and R⁵′ are members independently selected from the        group consisting of H, substituted alkyl, unsubstituted alkyl,        substituted aryl, unsubstituted aryl, substituted heteroaryl,        unsubstituted heteroaryl, substituted heterocycloalkyl,        unsubstituted heterocycloalkyl, halogen, NO₂, NR¹⁵R¹⁶, NC(O)R¹⁵,        OC(O)NR¹⁵R¹⁶, OC(O)OR¹⁵, C(O)R¹⁵, SR¹⁵, OR¹⁵, CR¹⁵═NR¹⁶, and        O(CH₂)_(n)NR²⁴R²⁵ wherein n is an integer from 1 to 20;    -   R¹⁵ and R¹⁶ are independently selected from H, substituted or        unsubstituted alkyl, substituted or unsubstituted heteroalkyl,        substituted or unsubstituted aryl, substituted or unsubstituted        heteroaryl, substituted or unsubstituted heterocycloalkyl, and        substituted or unsubstituted peptidyl, wherein R¹⁵ and R¹⁶        together with the nitrogen atom to which they are attached are        optionally joined to form a substituted or unsubstituted        heterocycloalkyl ring system having from 4 to 6 members,        optionally containing two or more heteroatoms;    -   and R²⁴ and R²⁵ are independently selected from unsubstituted        alkyl, and    -   wherein at least one of R⁴, R⁴′, R⁵ and R⁵′ is        O(CH₂)_(n)NR²⁴R²⁵.

In yet another aspect, the invention pertains to pharmaceuticalformulations. Such formulations typically comprise a conjugate compoundof the invention and a pharmaceutically acceptable carrier.

In still a further aspect, the invention pertains to methods of usingthe conjugate compounds of the invention. For example, the inventionprovides a method of killing a cell, wherein a conjugate compound of theinvention is administered to the cell an amount sufficient to kill thecell. In a preferred embodiment, the cell is a tumor cell. In anotherembodiment, the invention provides a method of retarding or stopping thegrowth of a tumor in a mammalian subject, wherein a conjugate compoundof the invention is administered to the subject an amount sufficient toretard or stop growth of the tumor.

Other aspects, advantages and objects of the invention will be apparentfrom review of the detailed description below.

DETAILED DESCRIPTION OF THE INVENTION Abbreviations

As used herein, “Ala,” refers to alanine.

“Boc,” refers to t-butyloxycarbonyl.

“CPI,” refers to cyclopropapyrroloindole.

“Cbz,” is carbobenzoxy.

As used herein, “DCM,” refers to dichloromethane.

“DDQ,” refers to 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.

DIPEA is diisopropylethalamine

“DMDA” is N,N′-dimethylethylene diamine

“RBF” is a round bottom flask

“DMF” is N,B-dimethylformamide

“HATU” isN-[[(dimethylamino)-1H-1,2,3-triazolo[4,5-b]pyridin-1-yl]methylene]-N-methylmethanaminiumhexafluorophosphate N-oxide

As used herein, the symbol “E,” represents an enzymatically cleaveablegroup.

“EDCI” is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide.

As used herein, “FMOC,” refers to 9-fluorenylmethyloxycarbonyl.

“FMOC” refers to 9-fluorenylmethoxycarbonyl.

“HOAt” is 7-Aza-1-hydroxybenzotriazole.

“Leu” is leucine.

“PABA” refers to para-aminobenzoic acid.

PEG refers to polyethylene glycol

“PMB,” refers to para-methoxybenzyl.

“TBAF,” refers to tetrabutylammonium fluoride.

The abbreviation “TBSO,” refers to t-butyldimethylsilyl ether.

As used herein, “TEA,” refers to triethylamine.

“TFA,” refers to trifluororoacetic acid.

The symbol “Q” refers to a therapeutic agent, diagnostic agent ordetectable label.

Definitions

Unless defined otherwise, all technical and scientific terms used hereingenerally have the same meaning as commonly understood by one ofordinary skill in the art to which this invention belongs. Generally,the nomenclature used herein and the laboratory procedures in cellculture, molecular genetics, organic chemistry and nucleic acidchemistry and hybridization described below are those well known andcommonly employed in the art. Standard techniques are used for nucleicacid and peptide synthesis. Generally, enzymatic reactions andpurification steps are performed according to the manufacturer'sspecifications. The techniques and procedures are generally performedaccording to conventional methods in the art and various generalreferences (see generally, Sambrook et al. MOLECULAR CLONING: ALABORATORY MANUAL, 2d ed. (1989) Cold Spring Harbor Laboratory Press,Cold Spring Harbor, N.Y., which is incorporated herein by reference),which are provided throughout this document. The nomenclature usedherein and the laboratory procedures in analytical chemistry, andorganic synthetic described below are those well known and commonlyemployed in the art. Standard techniques, or modifications thereof, areused for chemical syntheses and chemical analyses.

The term “therapeutic agent” is intended to mean a compound that, whenpresent in a therapeutically effective amount, produces a desiredtherapeutic effect on a mammal. For treating carcinomas, it is desirablethat the therapeutic agent also be capable of entering the target cell.

The term “cytotoxin” is intended to mean a therapeutic agent having thedesired effect of being cytotoxic to cancer cells. Cytotoxic means thatthe agent arrests the growth of, or kills the cells. Exemplarycytotoxins include, by way of example and not limitation,combretastatins, duocarmycins, the CC-1065 anti-tumor antibiotics,anthracyclines, and related compounds. Other cytotoxins includemycotoxins, ricin and its analogues, calicheamycins, doxirubicin andmaytansinoids.

The term “prodrug” and the term “drug conjugate” are used hereininterchangeably. Both refer to a compound that is relatively innocuousto cells while still in the conjugated form but which is selectivelydegraded to a pharmacologically active form by conditions, e.g.,enzymes, located within or in the proximity of target cells.

The term “marker” is intended to mean a compound useful in thecharacterization of tumors or other medical condition, for example,diagnosis, progression of a tumor, and assay of the factors secreted bytumor cells. Markers are considered a subset of “diagnostic agents.”

The term “selective” as used in connection with enzymatic cleavage meansthat the rate of rate of cleavage of the linker moiety is greater thanthe rate of cleavage of a peptide having a random sequence of aminoacids.

The terms “targeting group” and “targeting agent” are intended to mean amoiety that is (1) able to direct the entity to which it is attached(e.g., therapeutic agent or marker) to a target cell, for example to aspecific type of tumor cell or (2) is preferentially activated at atarget tissue, for example a tumor. The targeting group or targetingagent can be a small molecule, which is intended to include bothnon-peptides and peptides. The targeting group can also be amacromolecule, which includes saccharides, lectins, receptors, ligandfor receptors, proteins such as BSA, antibodies, and so forth. In apreferred embodiment of the current invention, the targeting group is anantibody or an antibody fragment, more preferably a monoclonal antibodyor monoclonal antibody fragment

The term “self-immolative spacer” refers to a bifunctional chemicalmoiety that is capable of covalently linking two chemical moieties intoa normally stable tripartate molecule. The self-immolative spacer iscapable of spontaneously separating from the second moiety if the bondto the first moiety is cleaved.

The term “detectable label” is intended to mean a moiety having adetectable physical or chemical property.

The term “cleaveable group” is intended to mean a moiety that isunstable in vivo. Preferably the “cleaveable group” allows foractivation of the marker or therapeutic agent by cleaving the marker oragent from the rest of the conjugate. Operatively defined, the linker ispreferably cleaved in vivo by the biological environment. The cleavagemay come from any process without limitation, e.g., enzymatic,reductive, pH, etc. Preferably, the cleaveable group is selected so thatactivation occurs at the desired site of action, which can be a site inor near the target cells (e.g., carcinoma cells) or tissues such as atthe site of therapeutic action or marker activity. Such cleavage may beenzymatic and exemplary enzymatically cleaveable groups include naturalamino acids or peptide sequences that end with a natural amino acid, andare attached at their carboxyl terminus to the linker. While the degreeof cleavage rate enhancement is not critical to the invention, preferredexamples of cleaveable linkers are those in which at least about 10% ofthe cleaveable groups are cleaved in the blood stream within 24 hours ofadministration, most preferably at least about 35%.

The term “ligand” means any molecule that specifically binds orreactively associates or complexes with a receptor, substrate, antigenicdeterminant, or other binding site on a target cell or tissue. Examplesof ligands include antibodies and fragments thereof (e.g., a monoclonalantibody or fragment thereof), enzymes (e.g., fibrinolytic enzymes),biologic response modifiers (e.g., interleukins, interferons,erythropeoitin, or colony stimulating factors), peptide hormones, andantigen-binding fragments thereof.

The terms “hydrazine linker” and “self-cyclizing hydrazine linker” areused interchangeably herein. These terms refer to a linker moiety that,upon a change in condition, such as a shift in pH, will undergo acyclization reaction and form one or more rings. The hydrazine moiety isconverted to a hydrazone when attached. This attachment can occur, forexample, through a reaction with a ketone group on the L⁴ moiety.Therefore, the term hydrazone linker can also be used to describe thelinker of the current invention because of this conversion to ahydrazone upon attachment.

The term “five-membered hydrazine linker” or “5-membered hydrazinelinker” refers to hydrazine-containing molecular moieties that, upon achange in condition, such as a shift in pH, will undergo a cyclizationreaction and form one or more 5-membered rings. Alternatively, this fivemembered linker may similarly be described as a five-membered hydrazonelinker or a 5-membered hydrazone linker.

The term “six-membered hydrazine linker” or “6-membered hydrazinelinker” refers to hydrazine-containing molecular moieties that, upon achange in condition such as a shift in pH, will undergo a cyclizationreaction and form one or more 6-membered rings. This six membered linkermay similarly be described as a six-membered hydrazone linker or a6-membered hydrazone linker.

The term “cyclization reaction,” when referring to the cyclization of apeptide, hydrazine, or disulfide linker, indicates the cyclization ofthat linker into a ring and initiates the separation of the drug-ligandcomplex. This rate can be measured ex situ, and is completed when atleast 90%, 95%, or 100% of the product is formed.

The terms “polypeptide,” “peptide” and “protein” are usedinterchangeably herein to refer to a polymer of amino acid residues. Theterms apply to amino acid polymers in which one or more amino acidresidue is an artificial chemical mimetic of a corresponding naturallyoccurring amino acid, as well as to naturally occurring amino acidpolymers and non-naturally occurring amino acid polymer. These termsalso encompass the term “antibody.”

The term “amino acid” refers to naturally occurring and synthetic aminoacids, as well as amino acid analogs and amino acid mimetics thatfunction in a manner similar to the naturally occurring amino acids.Naturally occurring amino acids are those encoded by the genetic code,as well as those amino acids that are later modified, e.g.,hydroxyproline, γ-carboxyglutamate, and O-phosphoserine. Amino acidanalogs refers to compounds that have the same basic chemical structureas a naturally occurring amino acid, i.e., an α carbon that is bound toa hydrogen, a carboxyl group, an amino group, and an R group, e.g.,homoserine, norleucine, methionine sulfoxide, methionine methylsulfonium. Such analogs have modified R groups (e.g., norleucine) ormodified peptide backbones, but retain the same basic chemical structureas a naturally occurring amino acid. One amino acid that may be used inparticular is citrulline, which is a precursor to arginine and isinvolved in the formation of urea in the liver. Amino acid mimeticsrefers to chemical compounds that have a structure that is differentfrom the general chemical structure of an amino acid, but functions in amanner similar to a naturally occurring amino acid. The term “unnaturalamino acid” is intended to represent the “D” stereochemical form of thetwenty naturally occurring amino acids described above. It is furtherunderstood that the term unnatural amino acid includes homologues of thenatural amino acids, and synthetically modified forms of the naturalamino acids. The synthetically modified forms include, but are notlimited to, amino acids having alkylene chains shortened or lengthenedby up to two carbon atoms, amino acids comprising optionally substitutedaryl groups, and amino acids comprised halogenated groups, preferablyhalogenated alkyl and aryl groups. When attached to a linker orconjugate of the invention, the amino acid is in the form of an “aminoacid side chain”, where the carboxylic acid group of the amino acid hasbeen replaced with a keto (C(O)) group. Thus, for example, an alanineside chain is —C(O)—CH(NH₂)—CH₃, and so forth.

Amino acids and peptides may be protected by blocking groups. A blockinggroup is an atom or a chemical moiety that protects the N-terminus of anamino acid or a peptide from undesired reactions and can be used duringthe synthesis of a drug-ligand conjugate. It should remain attached tothe N-terminus throughout the synthesis, and may be removed aftercompletion of synthesis of the drug conjugate by chemical or otherconditions that selectively achieve its removal. The blocking groupssuitable for N-terminus protection are well known in the art of peptidechemistry. Exemplary blocking groups include, but are not limited to,hydrogen, D-amino acid, and carbobenzoxy (Cbz) chloride.

“Nucleic acid” refers to deoxyribonucleotides or ribonucleotides andpolymers thereof in either single- or double-stranded form. The termencompasses nucleic acids containing known nucleotide analogs ormodified backbone residues or linkages, which are synthetic, naturallyoccurring, and non-naturally occurring, which have similar bindingproperties as the reference nucleic acid, and which are metabolized in amanner similar to the reference nucleotides. Examples of such analogsinclude, without limitation, phosphorothioates, phosphoramidates, methylphosphonates, chiral-methyl phosphonates, 2-O-methyl ribonucleotides,peptide-nucleic acids (PNAs).

Unless otherwise indicated, a particular nucleic acid sequence alsoimplicitly encompasses conservatively modified variants thereof (e.g.,degenerate codon substitutions) and complementary sequences, as well asthe sequence explicitly indicated. Specifically, degenerate codonsubstitutions may be achieved by generating sequences in which the thirdposition of one or more selected (or all) codons is substituted withmixed-base and/or deoxyinosine residues (Batzer et al., Nucleic AcidRes. 19:5081 (1991); Ohtsuka et al., J. Biol. Chem. 260: 2605-2608(1985); Rossolini et al., Mol. Cell. Probes 8: 91-98 (1994)). The termnucleic acid is used interchangeably with gene, cDNA, mRNA,oligonucleotide, and polynucleotide.

The symbol

, whether utilized as a bond or displayed perpendicular to a bondindicates the point at which the displayed moiety is attached to theremainder of the molecule, solid support, etc.

The term “alkyl,” by itself or as part of another substituent, means,unless otherwise stated, a straight or branched chain, or cyclichydrocarbon radical, or combination thereof, which may be fullysaturated, mono- or polyunsaturated and can include di- and multivalentradicals, having the number of carbon atoms designated (i.e. C₁-C₁₀means one to ten carbons). Examples of saturated hydrocarbon radicalsinclude, but are not limited to, groups such as methyl, ethyl, n-propyl,isopropyl, n-butyl, t-butyl, isobutyl, sec-butyl, cyclohexyl,(cyclohexyl)methyl, cyclopropylmethyl, homologs and isomers of, forexample, n-pentyl, n-hexyl, n-heptyl, n-octyl, and the like. Anunsaturated alkyl group is one having one or more double bonds or triplebonds. Examples of unsaturated alkyl groups include, but are not limitedto, vinyl, 2-propenyl, crotyl, 2-isopentenyl, 2-(butadienyl),2,4-pentadienyl, 3-(1,4-pentadienyl), ethynyl, 1- and 3-propynyl,3-butynyl, and the higher homologs and isomers. The term “alkyl,” unlessotherwise noted, is also meant to include those derivatives of alkyldefined in more detail below, such as “heteroalkyl.” Alkyl groups, whichare limited to hydrocarbon groups are termed “homo alkyl”.

The term “alkylene” by itself or as part of another substituent means adivalent radical derived from an alkane, as exemplified, but notlimited, by CH₂CH₂CH₂CH₂—, and further includes those groups describedbelow as “heteroalkylene.” Typically, an alkyl (or alkylene) group willhave from 1 to 24 carbon atoms, with those groups having 10 or fewercarbon atoms being preferred in the present invention. A “lower alkyl”or “lower alkylene” is a shorter chain alkyl or alkylene group,generally having eight or fewer carbon atoms.

The term “heteroalkyl,” by itself or in combination with another term,means, unless otherwise stated, a stable straight or branched chain, orcyclic hydrocarbon radical, or combinations thereof, consisting of thestated number of carbon atoms and at least one heteroatom selected fromthe group consisting of O, N, Si and S, and wherein the nitrogen, carbonand sulfur atoms may optionally be oxidized and the nitrogen heteroatommay optionally be quaternized. The heteroatom(s) O, N and S and Si maybe placed at any interior position of the heteroalkyl group or at theposition at which the alkyl group is attached to the remainder of themolecule. Examples include, but are not limited to, —CH₂—CH₂—O—CH₃,—CH₂—CH₂—NH—CH₃, —CH₂—CH₂—N(CH₃)—CH₃, —CH₂—S—CH₂—CH₃, —CH₂—CH₂,—S(O)—CH₃, —CH₂—CH₂—S(O)₂—CH₃, —CH═CH—O—CH₃, —Si(CH₃)₃, —CH₂—CH═N—OCH₃,and CH═CH—N(CH₃)—CH₃. Up to two heteroatoms may be consecutive, such as,for example, —CH₂—NH—OCH₃ and CH₂—O—Si(CH₃)₃. Similarly, the term“heteroalkylene” by itself or as part of another substituent means adivalent radical derived from heteroalkyl, as exemplified, but notlimited by, —CH₂—CH₂—S—CH₂—CH₂— and —CH₂—S—CH₂—CH₂—NH—CH₂—. Forheteroalkylene groups, heteroatoms can also occupy either or both of thechain termini (e.g., alkyleneoxy, alkylenedioxy, alkyleneamino,alkylenediamino, and the like). The terms “heteroalkyl” and“heteroalkylene” encompass poly(ethylene glycol) and its derivatives(see, for example, Shearwater Polymers Catalog, 2001). Still further,for alkylene and heteroalkylene linking groups, no orientation of thelinking group is implied by the direction in which the formula of thelinking group is written. For example, the formula C(O)₂R′— representsboth C(O)₂R′— and —R′C(O)₂—.

The term “lower” in combination with the terms “alkyl” or “heteroalkyl”refers to a moiety having from 1 to 6 carbon atoms.

The terms “alkoxy,” “alkylamino,” “alkylsulfonyl,” and “alkylthio” (orthioalkoxy) are used in their conventional sense, and refer to thosealkyl groups attached to the remainder of the molecule via an oxygenatom, an amino group, an SO₂ group or a sulfur atom, respectively. Theterm “arylsulfonyl” refers to an aryl group attached to the remainder ofthe molecule via an SO₂ group, and the term “sulfhydryl” refers to an SHgroup.

In general, an “acyl substituent” is also selected from the group setforth above. As used herein, the term “acyl substituent” refers togroups attached to, and fulfilling the valence of a carbonyl carbon thatis either directly or indirectly attached to the polycyclic nucleus ofthe compounds of the present invention.

The terms “cycloalkyl” and “heterocycloalkyl”, by themselves or incombination with other terms, represent, unless otherwise stated, cyclicversions of substituted or unsubstituted “alkyl” and substituted orunsubstituted “heteroalkyl”, respectively. Additionally, forheterocycloalkyl, a heteroatom can occupy the position at which theheterocycle is attached to the remainder of the molecule. Examples ofcycloalkyl include, but are not limited to, cyclopentyl, cyclohexyl,1-cyclohexenyl, 3-cyclohexenyl, cycloheptyl, and the like. Examples ofheterocycloalkyl include, but are not limited to,1-(1,2,5,6-tetrahydropyridyl), 1-piperidinyl, 2-piperidinyl,3-piperidinyl, 4-morpholinyl, 3-morpholinyl, tetrahydrofuran-2-yl,tetrahydrofuran-3-yl, tetrahydrothien-2-yl, tetrahydrothien-3-yl,1-piperazinyl, 2-piperazinyl, and the like. The heteroatoms and carbonatoms of the cyclic structures are optionally oxidized.

The terms “halo” or “halogen,” by themselves or as part of anothersubstituent, mean, unless otherwise stated, a fluorine, chlorine,bromine, or iodine atom. Additionally, terms such as “haloalkyl,” aremeant to include monohaloalkyl and polyhaloalkyl. For example, the term“halo(C₁-C₄)alkyl” is mean to include, but not be limited to,trifluoromethyl, 2,2,2-trifluoroethyl, 4-chlorobutyl, 3-bromopropyl, andthe like.

The term “aryl” means, unless otherwise stated, a substituted orunsubstituted polyunsaturated, aromatic, hydrocarbon substituent whichcan be a single ring or multiple rings (preferably from 1 to 3 rings)which are fused together or linked covalently. The term “heteroaryl”refers to aryl groups (or rings) that contain from one to fourheteroatoms selected from N, O, and S, wherein the nitrogen, carbon andsulfur atoms are optionally oxidized, and the nitrogen atom(s) areoptionally quaternized. A heteroaryl group can be attached to theremainder of the molecule through a heteroatom. Non-limiting examples ofaryl and heteroaryl groups include phenyl, 1-naphthyl, 2-naphthyl,4-biphenyl, 1-pyrrolyl, 2-pyrrolyl, 3-pyrrolyl, 3-pyrazolyl,2-imidazolyl, 4-imidazolyl, pyrazinyl, 2-oxazolyl, 4-oxazolyl,2-phenyl-4-oxazolyl, 5-oxazolyl, 3-isoxazolyl, 4-isoxazolyl,5-isoxazolyl, 2-thiazolyl, 4-thiazolyl, 5-thiazolyl, 2-furyl, 3-furyl,2-thienyl, 3-thienyl, 2-pyridyl, 3-pyridyl, 4-pyridyl, 2-pyrimidyl,4-pyrimidyl, 5-benzothiazolyl, purinyl, 2-benzimidazolyl, 5-indolyl,1-isoquinolyl, 5-isoquinolyl, 2-quinoxalinyl, 5-quinoxalinyl,3-quinolyl, and 6-quinolyl. Substituents for each of the above notedaryl and heteroaryl ring systems are selected from the group ofacceptable substituents described below. “Aryl” and “heteroaryl” alsoencompass ring systems in which one or more non-aromatic ring systemsare fused, or otherwise bound, to an aryl or heteroaryl system.

For brevity, the term “aryl” when used in combination with other terms(e.g., aryloxy, arylthioxy, arylalkyl) includes both aryl and heteroarylrings as defined above. Thus, the term “arylalkyl” is meant to includethose radicals in which an aryl group is attached to an alkyl group(e.g., benzyl, phenethyl, pyridylmethyl and the like) including thosealkyl groups in which a carbon atom (e.g., a methylene group) has beenreplaced by, for example, an oxygen atom (e.g., phenoxymethyl,2-pyridyloxymethyl, 3-(1-naphthyloxy)propyl, and the like).

Each of the above terms (e.g., “alkyl,” “heteroalkyl,” “aryl” and“heteroaryl”) include both substituted and unsubstituted forms of theindicated radical. Preferred substituents for each type of radical areprovided below.

Substituents for the alkyl, and heteroalkyl radicals (including thosegroups often referred to as alkylene, alkenyl, heteroalkylene,heteroalkenyl, alkynyl, cycloalkyl, heterocycloalkyl, cycloalkenyl, andheterocycloalkenyl) are generally referred to as “alkyl substituents”and “heteroalkyl substituents,” respectively, and they can be one ormore of a variety of groups selected from, but not limited to: —OR′, ═O,═NR′, ═N—OR′, —NR′R″, —SR′, -halogen, —SiR′R″R′″, —OC(O)R′, —C(O)R′,—CO₂R′, —CONR′R″, —OC(O)NR′R″, —NR″C(O)R′, —NR′—C(O)NR″R′″, —NR″C(O)₂R′,—NR—C(NR′R″R′″)═NR′″, —NR—C(NR′R″)═NR′″, —S(O)R′, —S(O)₂R′, —S(O)₂NR′R″,—NRSO₂R′, —CN and —NO₂ in a number ranging from zero to (2 m′+1), wherem′ is the total number of carbon atoms in such radical. R′, R″, R′″ andR″″ each preferably independently refer to hydrogen, substituted orunsubstituted heteroalkyl, substituted or unsubstituted aryl, e.g., arylsubstituted with 1-3 halogens, substituted or unsubstituted alkyl,alkoxy or thioalkoxy groups, or arylalkyl groups. When a compound of theinvention includes more than one R group, for example, each of the Rgroups is independently selected as are each R′, R″, R′″ and R″″ groupswhen more than one of these groups is present. When R′ and R″ areattached to the same nitrogen atom, they can be combined with thenitrogen atom to form a 5-, 6-, or 7-membered ring. For example, —NR′R″is meant to include, but not be limited to, 1-pyrrolidinyl and4-morpholinyl. From the above discussion of substituents, one of skillin the art will understand that the term “alkyl” is meant to includegroups including carbon atoms bound to groups other than hydrogengroups, such as haloalkyl (e.g., —CF₃ and —CH₂CF₃) and acyl (e.g.,—C(O)CH₃, —C(O)CF₃, —C(O)CH₂OCH₃, and the like).

Similar to the substituents described for the alkyl radical, the arylsubstituents and heteroaryl substituents are generally referred to as“aryl substituents” and “heteroaryl substituents,” respectively and arevaried and selected from, for example: halogen, —OR′, ═O, ═NR′, ═N—OR′,—NR′R″, —SR′, -halogen, —SiR′R″R′″, —OC(O)R′, —C(O)R′, —CO₂R′, —CONR′R″,—OC(O)NR′R″, —NR″C(O)R′, —NR′—C(O)NR″R′″, —NR″C(O)₂R′,—NR—C(NR′R″)═NR′″, —S(O)R′, —S(O)₂R′, —S(O)₂NR′R″, —NRSO₂R′, —CN andNO₂, —R′, —N₃, —CH(Ph)₂, fluoro(C₁-C₄)alkoxy, and fluoro(C₁-C₄)alkyl, ina number ranging from zero to the total number of open valences on thearomatic ring system; and where R′, R″, R′″ and R″″ are preferablyindependently selected from hydrogen, (C₁-C₈)alkyl and heteroalkyl,unsubstituted aryl and heteroaryl, (unsubstituted aryl)-(C₁-C₄)alkyl,and (unsubstituted aryl)oxy-(C₁-C₄)alkyl. When a compound of theinvention includes more than one R group, for example, each of the Rgroups is independently selected as are each R′, R″, R′″ and R″″ groupswhen more than one of these groups is present.

Two of the aryl substituents on adjacent atoms of the aryl or heteroarylring may optionally be replaced with a substituent of the formula-T-C(O)—(CRR′)_(q)—U—, wherein T and U are independently —NR—, —O—,—CRR′— or a single bond, and q is an integer of from 0 to 3.Alternatively, two of the substituents on adjacent atoms of the aryl orheteroaryl ring may optionally be replaced with a substituent of theformula -A-(CH₂)_(r)—B—, wherein A and B are independently —CRR′—, —O—,—NR—, —S—, —S(O)—, —S(O)₂—, —S(O)₂NR′— or a single bond, and r is aninteger of from 1 to 4. One of the single bonds of the new ring soformed may optionally be replaced with a double bond. Alternatively, twoof the substituents on adjacent atoms of the aryl or heteroaryl ring mayoptionally be replaced with a substituent of the formula—(CRR′)_(s)—X—(CR″R′″)_(d)—, where s and d are independently integers offrom 0 to 3, and X is —O—, —NR′—, —S—, —S(O)—, —S(O)₂—, or —S(O)₂NR′—.The substituents R, R′, R″ and R′″ are preferably independently selectedfrom hydrogen or substituted or unsubstituted (C₁-C₆) alkyl.

As used herein, the term “diphosphate” includes but is not limited to anester of phosphoric acid containing two phosphate groups. The term“triphosphate” includes but is not limited to an ester of phosphoricacid containing three phosphate groups. For example, particular drugshaving a diphosphate or a triphosphate include:

As used herein, the term “heteroatom” includes oxygen (O), nitrogen (N),sulfur (S) and silicon (Si).

The symbol “R” is a general abbreviation that represents a substituentgroup that is selected from substituted or unsubstituted alkyl,substituted or unsubstituted heteroalkyl, substituted or unsubstitutedaryl, substituted or unsubstituted heteroaryl, and substituted orunsubstituted heterocyclyl groups.

The term “pharmaceutically acceptable carrier”, as used herein means apharmaceutically-acceptable material, composition or vehicle, such as aliquid or solid filler, diluent, excipient, solvent or encapsulatingmaterial, involved in carrying or transporting a chemical agent.Pharmaceutically acceptable carriers include pharmaceutically acceptablesalts, where the term “pharmaceutically acceptable salts” includes saltsof the active compounds which are prepared with relatively nontoxicacids or bases, depending on the particular substituents found on thecompounds described herein. When compounds of the present inventioncontain relatively acidic functionalities, base addition salts can beobtained by contacting the neutral form of such compounds with asufficient amount of the desired base, either neat or in a suitableinert solvent. Examples of pharmaceutically acceptable base additionsalts include sodium, potassium, calcium, ammonium, organic amino, ormagnesium salt, or a similar salt. When compounds of the presentinvention contain relatively basic functionalities, acid addition saltscan be obtained by contacting the neutral form of such compounds with asufficient amount of the desired acid, either neat or in a suitableinert solvent. Examples of pharmaceutically acceptable acid additionsalts include those derived from inorganic acids like hydrochloric,hydrobromic, nitric, carbonic, monohydrogencarbonic, phosphoric,monohydrogenphosphoric, dihydrogenphosphoric, sulfuric,monohydrogensulfuric, hydriodic, or phosphorous acids and the like, aswell as the salts derived from relatively nontoxic organic acids likeacetic, propionic, isobutyric, maleic, malonic, benzoic, succinic,suberic, fumaric, lactic, mandelic, phthalic, benzenesulfonic,p-tolylsulfonic, citric, tartaric, methanesulfonic, and the like. Alsoincluded are salts of amino acids such as arginate and the like, andsalts of organic acids like glucuronic or galactunoric acids and thelike (see, for example, Berge et al., “Pharmaceutical Salts”, Journal ofPharmaceutical Science, 1977, 66, 1-19). Certain specific compounds ofthe present invention contain both basic and acidic functionalities thatallow the compounds to be converted into either base or acid additionsalts.

The neutral forms of the compounds are preferably regenerated bycontacting the salt with a base or acid and isolating the parentcompound in the conventional manner. The parent form of the compounddiffers from the various salt forms in certain physical properties, suchas solubility in polar solvents, but otherwise the salts are equivalentto the parent form of the compound for the purposes of the presentinvention.

In addition to salt forms, the present invention provides compounds,which are in a prodrug form. Prodrugs of the compounds described hereinare those compounds that readily undergo chemical changes underphysiological conditions to provide the compounds of the presentinvention. Additionally, prodrugs can be converted to the compounds ofthe present invention by chemical or biochemical methods in an ex vivoenvironment. For example, prodrugs can be slowly converted to thecompounds of the present invention when placed in a transdermal patchreservoir with a suitable enzyme or chemical reagent.

Certain compounds of the present invention can exist in unsolvated formsas well as solvated forms, including hydrated forms. In general, thesolvated forms are equivalent to unsolvated forms and are encompassedwithin the scope of the present invention. Certain compounds of thepresent invention may exist in multiple crystalline or amorphous forms.In general, all physical forms are equivalent for the uses contemplatedby the present invention and are intended to be within the scope of thepresent invention.

Certain compounds of the present invention possess asymmetric carbonatoms (optical centers) or double bonds; the racemates, diastereomers,geometric isomers and individual isomers are encompassed within thescope of the present invention.

The compounds of the present invention may also contain unnaturalproportions of atomic isotopes at one or more of the atoms thatconstitute such compounds. For example, the compounds may beradiolabeled with radioactive isotopes, such as for example tritium(³H), iodine-125 (¹²⁵I) or carbon-14 (¹⁴C). All isotopic variations ofthe compounds of the present invention, whether radioactive or not, areintended to be encompassed within the scope of the present invention.

The term “attaching moiety” or “moiety for attaching a targeting group”refers to a moiety which allows for attachment of a targeting group tothe linker. Typical attaching groups include, by way of illustration andnot limitation, alkyl, aminoalkyl, aminocarbonylalkyl, carboxyalkyl,hydroxyalkyl, alkyl-maleimide, alkyl-N-hydroxylsuccinimide,poly(ethylene glycol)-maleimide and poly(ethyleneglycol)-N-hydroxylsuccinimide, all of which may be further substituted.The linker can also have the attaching moiety be actually appended tothe targeting group.

As used herein, the term “leaving group” refers to a portion of asubstrate that is cleaved from the substrate in a reaction.

The term “antibody” as referred to herein includes whole antibodies andany antigen binding fragment (i.e., “antigen-binding portion”) or singlechains thereof. An “antibody” refers to a glycoprotein comprising atleast two heavy (H) chains and two light (L) chains inter-connected bydisulfide bonds, or an antigen binding portion thereof. Each heavy chainis comprised of a heavy chain variable region (V_(H)) and a heavy chainconstant region. The heavy chain constant region is comprised of threedomains, C_(H1), C_(H2) and C_(H3), and may be of the mu, delta, gamma,alpha or epsilon isotype. Each light chain is comprised of a light chainvariable region (V_(L)) and a light chain constant region. The lightchain constant region is comprised of one domain, C_(L), which may be ofthe kappa or lambda isotype. The V_(H) and V_(L) regions can be furthersubdivided into regions of hypervariability, termed complementaritydetermining regions (CDR), interspersed with regions that are moreconserved, termed framework regions (FR). Each V_(H) and V_(L) iscomposed of three CDRs and four FRs, arranged from amino-terminus tocarboxy-terminus in the following order: FR1, CDR1, FR2, CDR2, FR3,CDR3, FR4. The variable regions of the heavy and light chains contain abinding domain that interacts with an antigen. The constant regions ofthe antibodies may mediate the binding of the immunoglobulin to hosttissues or factors, including various cells of the immune system (e.g.,effector cells) and the first component (Clq) of the classicalcomplement system.

The terms “antibody fragment” or “antigen-binding portion” of anantibody (or simply “antibody portion”), as used herein, refers to oneor more fragments of an antibody that retain the ability to specificallybind to an antigen. It has been shown that the antigen-binding functionof an antibody can be performed by fragments of a full-length antibody.Examples of binding fragments encompassed within the term “antibodyfragment” or “antigen-binding portion” of an antibody include (i) a Fabfragment, a monovalent fragment consisting of the V_(L), V_(H), C_(L)and C_(H1) domains; (ii) a F(ab′)₂ fragment, a bivalent fragmentcomprising two Fab fragments linked by a disulfide bridge at the hingeregion; (iii) a Fd fragment consisting of the V_(H) and C_(H1) domains;(iv) a Fv fragment consisting of the V_(L) and V_(H) domains of a singlearm of an antibody, (v) a dAb fragment (Ward et al., (1989) Nature341:544-546), which consists of a V_(H) domain; and (vi) an isolatedcomplementarity determining region (CDR). Furthermore, although the twodomains of the Fv fragment, V_(L) and V_(H), are coded for by separategenes, they can be joined, using recombinant methods, by a syntheticlinker that enables them to be made as a single protein chain in whichthe V_(L) and V_(H) regions pair to form monovalent molecules (known assingle chain Fv (scFv); see e.g., Bird et al. (1988) Science242:423-426; and Huston et al. (1988) Proc. Natl. Acad. Sci. USA85:5879-5883). Such single chain antibodies are also intended to beencompassed within the term “antigen-binding portion” of an antibody.These antibody fragments are obtained using conventional techniquesknown to those with skill in the art, and the fragments are screened forutility in the same manner as are intact antibodies.

The terms “monoclonal antibody” as used herein refers to a preparationof antibody molecules of single molecular composition. A monoclonalantibody composition displays a single binding specificity and affinityfor a particular epitope.

For preparation of monoclonal or polyclonal antibodies, any techniqueknown in the art can be used (see, e.g., Kohler & Milstein, Nature256:495-497 (1975); Kozbor et al., Immunology Today 4: 72 (1983); Coleet al., pp. 77-96 in MONOCLONAL ANTIBODIES AND CANCER THERAPY, Alan R.Liss, Inc. (1985)).

Methods of production of polyclonal antibodies are known to those ofskill in the art. An inbred strain of mice (e.g., BALB/C mice) orrabbits is immunized with the protein using a standard adjuvant, such asFreund's adjuvant, and a standard immunization protocol. The animal'simmune response to the immunogen preparation is monitored by taking testbleeds and determining the titer of reactivity to the beta subunits.When appropriately high titers of antibody to the immunogen areobtained, blood is collected from the animal and antisera are prepared.Further fractionation of the antisera to enrich for antibodies reactiveto the protein can be done if desired.

Monoclonal antibodies may be obtained by various techniques familiar tothose skilled in the art. Briefly, spleen cells from an animal immunizedwith a desired antigen are immortalized, commonly by fusion with amyeloma cell (see Kohler & Milstein, Eur. J. Immunol. 6: 511-519(1976)). Alternative methods of immortalization include transformationwith Epstein Barr Virus, oncogenes, or retroviruses, or other methodswell known in the art.

In a preferred embodiment, the antibody is a chimeric or humanizedantibody. Chimeric or humanized antibodies of the present invention canbe prepared based on the sequence of a murine monoclonal antibody. DNAencoding the heavy and light chain immunoglobulins can be obtained fromthe murine hybridoma of interest and engineered to contain non-murine(e.g., human) immunoglobulin sequences using standard molecular biologytechniques. For example, to create a chimeric antibody, the murinevariable regions can be linked to human constant regions using methodsknown in the art (see e.g., U.S. Pat. No. 4,816,567 to Cabilly et al.).To create a humanized antibody, the murine CDR regions can be insertedinto a human framework using methods known in the art (see e.g., U.S.Pat. No. 5,225,539 to Winter, and U.S. Pat. Nos. 5,530,101; 5,585,089;5,693,762 and 6,180,370 to Queen et al.).

In another preferred embodiment, the antibody is a human antibody. Suchhuman antibodies can be generated by immunizing transgenic ortranschromosomic mice in which the endogenous mouse immunoglobulin geneshave been inactivated and exogenous human immunoglobulin genes have beenintroduced. Such mice are known in the art (see e.g., U.S. Pat. Nos.5,545,806; 5,569,825; 5,625,126; 5,633,425; 5,789,650; 5,877,397;5,661,016; 5,814,318; 5,874,299; and 5,770,429; all to Lonberg and Kay;U.S. Pat. Nos. 5,939,598; 6,075,181; 6,114,598; 6,150,584 and 6,162,963to Kucherlapati et al.; and PCT Publication WO 02/43478 to Ishida etal.) Human antibodies can also be prepared using phage display methodsfor screening libraries of human immunoglobulin genes. Such phagedisplay methods for isolating human antibodies also are know in the art(see e.g., U.S. Pat. Nos. 5,223,409; 5,403,484; and 5,571,698 to Ladneret al.; U.S. Pat. Nos. 5,427,908 and 5,580,717 to Dower et al.; U.S.Pat. Nos. 5,969,108 and 6,172,197 to McCafferty et al.; and U.S. Pat.Nos. 5,885,793; 6,521,404; 6,544,731; 6,555,313; 6,582,915 and 6,593,081to Griffiths et al.).

“Solid support,” as used herein refers to a material that issubstantially insoluble in a selected solvent system, or which can bereadily separated (e.g., by precipitation) from a selected solventsystem in which it is soluble. Solid supports useful in practicing thepresent invention can include groups that are activated or capable ofactivation to allow selected species to be bound to the solid support. Asolid support can also be a substrate, for example, a chip, wafer orwell, onto which an individual, or more than one compound, of theinvention is bound.

“Reactive functional group,” as used herein refers to groups including,but not limited to, olefins, acetylenes, alcohols, phenols, ethers,oxides, halides, aldehydes, ketones, carboxylic acids, esters, amides,cyanates, isocyanates, thiocyanates, isothiocyanates, amines,hydrazines, hydrazones, hydrazides, diazo, diazonium, nitro, nitriles,mercaptans, sulfides, disulfides, sulfoxides, sulfones, sulfonic acids,sulfinic acids, acetals, ketals, anhydrides, sulfates, sulfenic acidsisonitriles, amidines, imides, imidates, nitrones, hydroxylamines,oximes, hydroxamic acids thiohydroxamic acids, allenes, ortho esters,sulfites, enamines, ynamines, ureas, pseudoureas, semicarbazides,carbodiimides, carbamates, imines, azides, azo compounds, azoxycompounds, and nitroso compounds. Reactive functional groups alsoinclude those used to prepare bioconjugates, e.g., N-hydroxysuccinimideesters, maleimides and the like (see, for example, Hermanson,BIOCONJUGATE TECHNIQUES, Academic press, San Diego, 1996). Methods toprepare each of these functional groups are well known in the art andtheir application to or modification for a particular purpose is withinthe ability of one of skill in the art (see, for example, Sandler andKaro, eds. ORGANIC FUNCTIONAL GROUP PREPARATIONS, Academic Press, SanDiego, 1989). The reactive functional groups may be protected orunprotected.

The compounds of the invention are prepared as a single isomer (e.g.,enantiomer, cis-trans, positional, diastereomer) or as a mixture ofisomers. In a preferred embodiment, the compounds are prepared assubstantially a single isomer. Methods of preparing substantiallyisomerically pure compounds are known in the art. For example,enantiomerically enriched mixtures and pure enantiomeric compounds canbe prepared by using synthetic intermediates that are enantiomericallypure in combination with reactions that either leave the stereochemistryat a chiral center unchanged or result in its complete inversion.Alternatively, the final product or intermediates along the syntheticroute can be resolved into a single stereoisomer. Techniques forinverting or leaving unchanged a particular stereocenter, and those forresolving mixtures of stereoisomers are well known in the art and it iswell within the ability of one of skill in the art to choose andappropriate method for a particular situation. See, generally, Furnisset al. (eds.), VOGEL'S ENCYCLOPEDIA OF PRACTICAL ORGANIC CHEMISTRY5^(TH) ED., Longman Scientific and Technical Ltd., Essex, 1991, pp.809-816; and Heller, Acc. Chem. Res. 23: 128 (1990).

Linkers

The present invention provides for drug-ligand conjugates where the drugis linked to the ligand through a chemical linker. This linker is eithera peptidyl, hydrazine, or disulfide linker, and is depicted herein as(L⁴)_(p)-F-(L¹)_(m), (L⁴)_(p)-H-(L¹)_(m), or (L⁴)_(p)-J-(L¹)_(m),respectively. In addition to the linkers as being attached to the drug,the present invention also provides cleaveable linker arms that areappropriate for attachment to essentially any molecular species. Thelinker arm aspect of the invention is exemplified herein by reference totheir attachment to a therapeutic moiety. It will, however, be readilyapparent to those of skill in the art that the linkers can be attachedto diverse species including, but not limited to, diagnostic agents,analytical agents, biomolecules, targeting agents, detectable labels andthe like.

In one aspect, the present invention relates to linkers that are usefulto attach targeting groups to therapeutic agents and markers. In anotheraspect, the invention provides linkers that impart stability tocompounds, reduce their in vivo toxicity, or otherwise favorably affecttheir pharmacokinetics, bioavailability and/or pharmacodynamics. It isgenerally preferred that in such embodiments, the linker is cleaved,releasing the active drug, once the drug is delivered to its site ofaction. Thus, in one embodiment of the invention, the linkers of theinvention are traceless, such that once removed from the therapeuticagent or marker (such as during activation), no trace of the linker'spresence remains.

In another embodiment of the invention, the linkers are characterized bytheir ability to be cleaved at a site in or near the target cell such asat the site of therapeutic action or marker activity. Such cleavage canbe enzymatic in nature. This feature aids in reducing systemicactivation of the therapeutic agent or marker, reducing toxicity andsystemic side effects. Preferred cleaveable groups for enzymaticcleavage include peptide bonds, ester linkages, and disulfide linkages.In other embodiments, the linkers are sensitive to pH and are cleavedthrough changes in pH.

An important aspect of the current invention is the ability to controlthe speed with which the linkers cleave. For example, the hydrazinelinkers described herein are particularly useful because, depending onwhich particular structure is used, one can vary the speed at which thelinker cyclizes and thereby cleaves the drug from the ligand. WO02/096910 provides several specific ligand-drug complexes having ahydrazine linker. However, there is no way to “tune” the linkercomposition dependent upon the rate of cyclization required, and theparticular compounds described cleave the ligand from the drug at aslower rate than is preferred for many drug-linker conjugates. Incontrast, the hydrazine linkers of the current invention provide for arange of cyclization rates, from very fast to very slow, therebyallowing for the selection of a particular hydrazine linker based on thedesired rate of cyclization. For example, very fast cyclization can beachieved with hydrazine linkers that produce a single 5-membered ringupon cleavage. Preferred cyclization rates for targeted delivery of acytotoxic agent to cells are achieved using hydrazine linkers thatproduce, upon cleavage, either two 5-membered rings or a single6-membered ring resulting from a linker having two methyls at thegeminal position. The gem-dimethyl effect has been shown to acceleratethe rate of the cyclization reaction as compared to a single 6-memberedring without the two methyls at the geminal position. This results fromthe strain being relieved in the ring. Sometimes, however, substitutentsmay slow down the reaction instead of making it faster. Often thereasons for the retardation can be traced to steric hindrance. As shownin Example 2.4, the gem dimethyl substitution allows for a much fastercyclization reaction to occur compared to when the geminal carbon is aCH₂.

It is important to note, however, that in some embodiments, a linkerthat cleaves more slowly may be preferred. For example, in a sustainedrelease formulation or in a formulation with both a quick release and aslow release component, it may be useful to provide a linker whichcleaves more slowly. In certain embodiments, a slow rate of cyclizationis achieved using a hydrazine linker that produces, upon cleavage,either a single 6-membered ring, without the gem-dimethyl substitution,or a single 7-membered ring.

The linkers also serve to stabilize the therapeutic agent or markeragainst degradation while in circulation. This feature provides asignificant benefit since such stabilization results in prolonging thecirculation half-life of the attached agent or marker. The linker alsoserves to attenuate the activity of the attached agent or marker so thatthe conjugate is relatively benign while in circulation and has thedesired effect, for example is toxic, after activation at the desiredsite of action. For therapeutic agent conjugates, this feature of thelinker serves to improve the therapeutic index of the agent.

The stabilizing groups are preferably selected to limit clearance andmetabolism of the therapeutic agent or marker by enzymes that may bepresent in blood or non-target tissue and are further selected to limittransport of the agent or marker into the cells. The stabilizing groupsserve to block degradation of the agent or marker and may also act inproviding other physical characteristics of the agent or marker. Thestabilizing group may also improve the agent or marker's stabilityduring storage in either a formulated or non-formulated form.

Ideally, the stabilizing group is useful to stabilize a therapeuticagent or marker if it serves to protect the agent or marker fromdegradation when tested by storage of the agent or marker in human bloodat 37° C. for 2 hours and results in less than 20%, preferably less than10%, more preferably less than 5% and even more preferably less than 2%,cleavage of the agent or marker by the enzymes present in the humanblood under the given assay conditions.

The present invention also relates to conjugates containing theselinkers. More particularly, the invention relates to prodrugs that maybe used for the treatment of disease, especially for cancerchemotherapy. Specifically, use of the linkers described herein providefor prodrugs that display a high specificity of action, a reducedtoxicity, and an improved stability in blood relative to prodrugs ofsimilar structure.

The linkers of the present invention as described herein may be presentat any position within the cytotoxic conjugate.

Thus, there is provided a linker that may contain any of a variety ofgroups as part of its chain that will cleave in vivo, e.g., in the bloodstream at a rate which is enhanced relative to that of constructs thatlack such groups. Also provided are conjugates of the linker arms withtherapeutic and diagnostic agents. The linkers are useful to formprodrug analogs of therapeutic agents and to reversibly link atherapeutic or diagnostic agent to a targeting agent, a detectablelabel, or a solid support. The linkers may be incorporated intocomplexes that include the cytotoxins of the invention.

In addition to the cleaveable peptide, hydrazine, or disulfide group,one or more self-immolative linker groups L¹ are optionally introducedbetween the cytotoxin and the targeting agent. These linker groups mayalso be described as spacer groups and contain at least two reactivefunctional groups. Typically, one chemical functionality of the spacergroup bonds to a chemical functionality of the therapeutic agent, e.g.,cytotoxin, while the other chemical functionality of the spacer group isused to bond to a chemical functionality of the targeting agent or thecleaveable linker. Examples of chemical functionalities of spacer groupsinclude hydroxy, mercapto, carbonyl, carboxy, amino, ketone, andmercapto groups.

The self-immolative linkers, represented by L¹, are generallysubstituted or unsubstituted alkyl, substituted or unsubstituted aryl,substituted or unsubstituted heteroaryl or a substituted orunsubstituted heteroalkyl group. In one embodiment, the alkyl or arylgroups may comprise between 1 and 20 carbon atoms. They may alsocomprise a polyethylene glycol moiety.

Exemplary spacer groups include, for example, 6-aminohexanol,6-mercaptohexanol, 10-hydroxydecanoic acid, glycine and other aminoacids, 1,6-hexanediol, (3-alanine, 2-aminoethanol,cysteamine(2-aminoethanethiol), 5-aminopentanoic acid, 6-aminohexanoicacid, 3-maleimidobenzoic acid, phthalide, α-substituted phthalides, thecarbonyl group, aminal esters, nucleic acids, peptides and the like.

The spacer can serve to introduce additional molecular mass and chemicalfunctionality into the cytotoxin-targeting agent complex. Generally, theadditional mass and functionality will affect the serum half-life andother properties of the complex. Thus, through careful selection ofspacer groups, cytotoxin complexes with a range of serum half-lives canbe produced.

The spacer(s) located directly adjacent to the drug moiety is alsodenoted as (L¹)_(m), wherein m is an integer selected from 0, 1, 2, 3,4, 5, or 6. When multiple L¹ spacers are present, either identical ordifferent spacers may be used. L¹ may be any self-immolative group. Inone embodiment, L¹ is preferably is a substituted alkyl, unsubstitutedalkyl, substituted heteroalkyl, and unsubstituted heteroalkyl,unsubstituted heterocycloalkyl, and substituted heterocycloalkyl. Whenthe drug-ligand conjugate comprises a hydrazine linker, L¹ does notcomprise a disulfide bond.

L⁴ is a linker moiety that imparts increased solubility or decreasedaggregation properties to conjugates utilizing a linker that containsthe moiety. The L⁴ linker does not have to be self immolative. In oneembodiment, the L⁴ moiety is substituted alkyl, unsubstituted alkyl,substituted aryl, unsubstituted aryl, substituted heteroalkyl, orunsubstituted heteroalkyl, any of which may be straight, branched, orcyclic. The substitutions may be, for example, a lower (C¹-C⁶) alkyl,alkoxy, aldylthio, alkylamino, or dialkylamino. In certain embodiments,L⁴ comprises a non-cyclic moiety. In another embodiment, L⁴ comprisesany positively or negatively charged amino acid polymer, such aspolylysine or polyargenine. L⁴ can comprise a polymer such as apolyethylene glycol moiety. Additionally the L⁴ linker comprises, forexample, both a polymer component and a small chemical moiety.

In a preferred embodiment, L⁴ comprises a polyethylene glycol (PEG)moiety. The PEG portion of L⁴ may be between 1 and 50 units long.Preferably, the PEG will have 1-12 repeat units, more preferably 3-12repeat units, more preferably 2-6 repeat units, or even more preferably3-5 repeat units and most preferably 4 repeat units. L⁴ may consistsolely of the PEG moiety, or it may also contain an additionalsubstituted or unsubstituted alkyl or heteroalkyl. It is useful tocombine PEG as part of the L⁴ moiety to enhance the water solubility ofthe complex. Additionally, the PEG moiety reduces the degree ofaggregation that may occur during the conjugation of the drug to theantibody.

(1) Peptide Linkers (F)

As discussed above, the peptidyl linkers of the invention can berepresented by the general formula: (L⁴)_(p)-F-(L¹)_(m), wherein Frepresents the linker portion comprising the peptidyl moiety. In oneembodiment, the F portion comprises an optional additionalself-immolative linker(s), L², and a carbonyl group. In anotherembodiment, the F portion comprises an amino group and an optionalspacer group(s), L³.

Accordingly, in one embodiment, the conjugate comprising the peptidyllinker comprises a structure of the Formula 4:

In this embodiment, L¹ is a self-immolative linker, as described above,and L⁴ is a moiety that imparts increased solubility, or decreasedaggregation properties, as described above. L² represents aself-immolative linker(s). m is 0, 1, 2, 3, 4, 5, or 6; o and p areindependently 0 or 1. In one embodiment, m is 3, 4, 5 or 6. AA¹represents one or more natural amino acids, and/or unnatural α-aminoacids; c is an integer between 1 and 20.

In the peptide linkers of the invention of the above Formula 4, AA¹ islinked, at its amino terminus, either directly to L⁴ or, when L⁴ isabsent, directly to the X⁴ group (i.e., the targeting agent, detectablelabel, protected reactive functional group or unprotected reactivefunctional group). In some embodiments, when L⁴ is present, L⁴ does notcomprise a carboxylic acyl group directly attached to the N-terminus of(AA¹)_(c). Thus, it is not necessary in these embodiments for there tobe a carboxylic acyl unit directly between either L⁴ or X⁴ and AA¹, asis necessary in the peptidic linkers of U.S. Pat. No. 6,214,345.

In another embodiment, the conjugate comprising the peptidyl linkercomprises a structure of the Formula 5:

In this embodiment, L⁴ is a moiety that imparts increased solubility, ordecreased aggregation properties, as described above; L³ is a spacergroup comprising a primary or secondary amine or a carboxyl functionalgroup, and either the amine of L³ forms an amide bond with a pendantcarboxyl functional group of D or the carboxyl of L³ forms an amide bondwith a pendant amine functional group of D; and o and p areindependently 0 or 1. AA¹ represents one or more natural amino acids,and/or unnatural α-amino acids; c is an integer between 1 and 20. Inthis embodiment, L¹ is absent (i.e., m is 0 is the general formula).

In the peptide linkers of the invention of the above Formula 5, AA¹ islinked, at its amino terminus, either directly to L⁴ or, when L⁴ isabsent, directly to the X⁴ group (i.e., the targeting agent, detectablelabel, protected reactive functional group or unprotected reactivefunctional group). In some embodiments, when L⁴ is present, L⁴ does notcomprise a carboxylic acyl group directly attached to the N-terminus of(AA¹)_(c). Thus, it is not necessary in these embodiments for there tobe a carboxylic acyl unit directly between either L⁴ or X⁴ and AA¹, asis necessary in the peptidic linkers of U.S. Pat. No. 6,214,345.

The Self-Immolative Linker L²

The self-immolative linker L² is a bifunctional chemical moiety which iscapable of covalently linking together two spaced chemical moieties intoa normally stable tripartate molecule, releasing one of said spacedchemical moieties from the tripartate molecule by means of enzymaticcleavage; and following said enzymatic cleavage, spontaneously cleavingfrom the remainder of the molecule to release the other of said spacedchemical moieties. In accordance with the present invention, theself-immolative spacer is covalently linked at one of its ends to thepeptide moiety and covalently linked at its other end to the chemicalreactive site of the drug moiety whose derivatization inhibitspharmacological activity, so as to space and covalently link togetherthe peptide moiety and the drug moiety into a tripartate molecule whichis stable and pharmacologically inactive in the absence of the targetenzyme, but which is enzymatically cleavable by such target enzyme atthe bond covalently linking the spacer moiety and the peptide moiety tothereby effect release of the peptide moiety from the tripartatemolecule. Such enzymatic cleavage, in turn, will activate theself-immolating character of the spacer moiety and initiate spontaneouscleavage of the bond covalently linking the spacer moiety to the drugmoiety, to thereby effect release of the drug in pharmacologicallyactive form.

The self-immolative linker L² may be any self-immolative group.Preferably L² is a substituted alkyl, unsubstituted alkyl, substitutedheteroalkyl, unsubstituted heteroalkyl, unsubstituted heterocycloalkyl,substituted heterocycloalkyl, substituted and unsubstituted aryl, andsubstituted and unsubstituted heteroaryl.

One particularly preferred self-immolative spacer L² may be representedby the formula 6:

The aromatic ring of the aminobenzyl group may be substituted with oneor more “K” groups. A “K” group is a substituent on the aromatic ringthat replaces a hydrogen otherwise attached to one of the fournon-substituted carbons that are part of the ring structure. The “K”group may be a single atom, such as a halogen, or may be a multi-atomgroup, such as alkyl, heteroalkyl, amino, nitro, hydroxy, alkoxy,haloalkyl, and cyano. Each K is independently selected from the groupconsisting of substituted alkyl, unsubstituted alkyl, substitutedheteroalkyl, unsubstituted heteroalkyl, substituted aryl, unsubstitutedaryl, substituted heteroaryl, unsubstituted heteroaryl, substitutedheterocycloalkyl, unsubstituted heterocycloalkyl, halogen, NO₂, NR²¹R²²,NR²¹COR²², OCONR²¹R²², OCOR²¹, and OR²¹, wherein R²¹ and R²² areindependently selected from the group consisting of H, substitutedalkyl, unsubstituted alkyl, substituted heteroalkyl, unsubstitutedheteroalkyl, substituted aryl, unsubstituted aryl, substitutedheteroaryl, unsubstituted heteroaryl, substituted heterocycloalkyl andunsubstituted heterocycloalkyl. Exemplary K substituents include, butare not limited to, F, Cl, Br, I, NO₂, OH, OCH₃, NHCOCH₃, N(CH₃)₂,NHCOCF₃ and methyl. For “Ka”, a is an integer of 0, 1, 2, 3, or 4. Inone preferred embodiment, a is 0.

The ether oxygen atom of the structure shown above is connected to acarbonyl group. The line from the NR²⁴ functionality into the aromaticring indicates that the amine functionality may be bonded to any of thefive carbons that both form the ring and are not substituted by theCH₂—O— group. Preferably, the NR²⁴ functionality of X is covalentlybound to the aromatic ring at the para position relative to the —CH₂—O—group. R²⁴ is a member selected from the group consisting of H,substituted alkyl, unsubstituted alkyl, substituted heteroalkyl, andunsubstituted heteroalkyl. In a specific embodiment, R²⁴ is hydrogen.

In a preferred embodiment, the invention provides a peptide linker offormula (4) above, wherein F comprises the structure:

wherein

-   -   R²⁴ is selected from the group consisting of H, substituted        alkyl, unsubstituted alkyl, substituted heteroalkyl, and        unsubstituted heteroalkyl;    -   Each K is a member independently selected from the group        consisting of substituted alkyl, unsubstituted alkyl,        substituted heteroalkyl, unsubstituted heteroalkyl, substituted        aryl, unsubstituted aryl, substituted heteroaryl, unsubstituted        heteroaryl, substituted heterocycloalkyl, unsubstituted        heterocycloalkyl, halogen, NO₂, NR²¹R²², NR²¹COR²², OCONR²¹R²²,        OCOR²¹, and OR²¹

wherein

-   -   R²¹ and R²² are independently selected from the group consisting        of H, substituted alkyl, unsubstituted alkyl, substituted        heteroalkyl, unsubstituted heteroalkyl, substituted aryl,        unsubstituted aryl, substituted heteroaryl, unsubstituted        heteroaryl, substituted heterocycloalkyl, unsubstituted        heterocycloalkyl; and    -   a is an integer of 0, 1, 2, 3, or 4.

In another embodiment, the peptide linker of formula (4) above comprisesa —F-(L¹)_(m)- that comprises the structure:

wherein

-   -   each R²⁴ is a member independently selected from the group        consisting of H, substituted alkyl, unsubstituted alkyl,        substituted heteroalkyl, and unsubstituted heteroalkyl.        The Spacer Group L³

The spacer group L³ is characterized in that it comprises a primary orsecondary amine or a carboxyl functional group, and either the amine ofthe L³ group forms an amide bond with a pendant carboxyl functionalgroup of D or the carboxyl of L³ forms an amide bond with a pendantamine functional group of D. L³ can be selected from the groupconsisting of substituted or unsubstituted alkyl, substituted orunsubstituted heteroalkyl, substituted or unsubstituted aryl,substituted or unsubstituted heteroaryl, or substituted or unsubstitutedheterocycloalkyl. In a preferred embodiment, L³ comprises an aromaticgroup. More preferably, L³ comprises a benzoic acid group, an anilinegroup or indole group. Non-limiting examples of structures that canserve as an -L³-NH— spacer include the following structures:

wherein Z is a member selected from O, S and NR²³, and

wherein R²³ is a member selected from H, substituted or unsubstitutedalkyl, substituted or unsubstituted heteroalkyl, and acyl.

Upon cleavage of the linker of the invention containing L³, the L³moiety remains attached to the drug, D. Accordingly, the L³ moiety ischosen such that its presence attached to D does not significantly alterthe activity of D. In another embodiment, a portion of the drug D itselffunctions as the L³ spacer. For example, in one embodiment, the drug, D,is a duocarmycin derivative in which a portion of the drug functions asthe L³ spacer. Non-limiting examples of such embodiments include thosein which NH₂-(L³)-D has a structure selected from the group consistingof:

wherein Z is a member selected from O, S and NR²³,

wherein R²³ is a member selected from H, substituted or unsubstitutedalkyl, substituted or unsubstituted heteroalkyl, and acyl; and

wherein the NH₂ group on each structure reacts with (AA¹)_(c) to form(AA¹)_(c)-NH—.

The Peptide Sequence AA¹

The group AA¹ represents a single amino acid or a plurality of aminoacids that are joined together by amide bonds. The amino acids may benatural amino acids and/or unnatural α-amino acids.

The peptide sequence (AA¹)_(c) is functionally the amidification residueof a single amino acid (when c=1) or a plurality of amino acids joinedtogether by amide bonds. The peptide of the current invention isselected for directing enzyme-catalyzed cleavage of the peptide by anenzyme in a location of interest in a biological system. For example,for conjugates that are targeted to a cell using a targeting agent, andthen taken up by the cell, a peptide is chosen that is cleaved by one ormore lysosomal proteases such that the peptide is cleavedintracellularly within the lysosome. The number of amino acids withinthe peptide can range from 1 to 20; but more preferably there will be2-8 amino acids, 2-6 amino acids or 2, 3 or 4 amino acids comprising(AA¹)_(c). Peptide sequences that are susceptible to cleavage byspecific enzymes or classes of enzymes are well known in the art.

Many peptide sequences that are cleaved by enzymes in the serum, liver,gut, etc. are known in the art. An exemplary peptide sequence of theinvention includes a peptide sequence that is cleaved by a protease. Thefocus of the discussion that follows on the use of a protease-sensitivesequence is for clarity of illustration and does not serve to limit thescope of the present invention.

When the enzyme that cleaves the peptide is a protease, the linkergenerally includes a peptide containing a cleavage recognition sequencefor the protease. A cleavage recognition sequence for a protease is aspecific amino acid sequence recognized by the protease duringproteolytic cleavage. Many protease cleavage sites are known in the art,and these and other cleavage sites can be included in the linker moiety.See, e.g., Matayoshi et al. Science 247: 954 (1990); Dunn et al. Meth.Enzymol. 241: 254 (1994); Seidah et al. Meth. Enzymol. 244: 175 (1994);Thornberry, Meth. Enzymol. 244: 615 (1994); Weber et al. Meth. Enzymol.244: 595 (1994); Smith et al. Meth. Enzymol. 244: 412 (1994); Bouvier etal. Meth. Enzymol. 248: 614 (1995), Hardy et al., in AMYLOID PROTEINPRECURSOR IN DEVELOPMENT, AGING, AND ALZHEIMER'S DISEASE, ed. Masters etal. pp. 190-198 (1994).

The amino acids of the peptide sequence (AA¹)_(c) are chosen based ontheir suitability for selective enzymatic cleavage by particularmolecules such as tumor-associated protease. The amino acids used may benatural or unnatural amino acids. They may be in the L or the Dconfiguration. In one embodiment, at least three different amino acidsare used. In another embodiment, only two amino acids are used.

In a preferred embodiment, the peptide sequence (AA¹)_(c) is chosenbased on its ability to be cleaved by a lysosomal proteases,non-limiting examples of which include cathepsins B, C, D, H, L and S.Preferably, the peptide sequence (AA¹)_(c) is capable of being cleavedby cathepsin B in vitro, which can be tested using in vitro proteasecleavage assays known in the art.

In another embodiment, the peptide sequence (AA¹)_(c) is chosen based onits ability to be cleaved by a tumor-associated protease, such as aprotease that is found extracellularly in the vicinity of tumor cells,non-limiting examples of which include thimet oligopeptidase (TOP) andCD10. The ability of a peptide to be cleaved by TOP or CD10 can betested using in vitro protease cleavage assays known in the art.

Suitable, but non-limiting, examples of peptide sequences suitable foruse in the conjugates of the invention include Val-Cit, Val-Lys,Phe-Lys, Lys-Lys, Ala-Lys, Phe-Cit, Leu-Cit, Ile-Cit, Trp, Cit, Phe-Ala,Phe-N⁹-tosyl-Arg, Phe-N⁹-nitro-Arg, Phe-Phe-Lys, D-Phe-Phe-Lys,Gly-Phe-Lys, Leu-Ala-Leu, Ile-Ala-Leu, Val-Ala-Val, Ala-Leu-Ala-Leu (SEQID NO: 1), 13-Ala-Leu-Ala-Leu (SEQ ID NO: 2) and Gly-Phe-Leu-Gly (SEQ IDNO: 3). Preferred peptides sequences are Val-Cit and Val-Lys.

In another embodiment, the amino acid located the closest to the drugmoiety is selected from the group consisting of Ala, Asn, Asp, Cit, Cys,Gln, Glu, Gly, Ile, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Tyr, andVal. In yet another embodiment, the amino acid located the closest tothe drug moiety is selected from the group consisting of: Ala, Asn, Asp,Cys, Gln, Glu, Gly, Ile, Leu, Met, Phe, Pro, Ser, Thr, Trp, Tyr, andVal.

Proteases have been implicated in cancer metastasis. Increased synthesisof the protease urokinase was correlated with an increased ability tometastasize in many cancers. Urokinase activates plasmin fromplasminogen, which is ubiquitously located in the extracellular spaceand its activation can cause the degradation of the proteins in theextracellular matrix through which the metastasizing tumor cells invade.Plasmin can also activate the collagenases thus promoting thedegradation of the collagen in the basement membrane surrounding thecapillaries and lymph system thereby allowing tumor cells to invade intothe target tissues (Dano, et al. Adv. Cancer. Res., 44: 139 (1985)).Thus, it is within the scope of the present invention to utilize as alinker a peptide sequence that is cleaved by urokinase.

The invention also provides the use of peptide sequences that aresensitive to cleavage by tryptases. Human mast cells express at leastfour distinct tryptases, designated αβI, βII, and βIII. These enzymesare not controlled by blood plasma proteinase inhibitors and only cleavea few physiological substrates in vitro. The tryptase family of serineproteases has been implicated in a variety of allergic and inflammatorydiseases involving mast cells because of elevated tryptase levels foundin biological fluids from patients with these disorders. However, theexact role of tryptase in the pathophysiology of disease remains to bedelineated. The scope of biological functions and correspondingphysiological consequences of tryptase are substantially defined bytheir substrate specificity.

Tryptase is a potent activator of pro-urokinase plasminogen activator(uPA), the zymogen form of a protease associated with tumor metastasisand invasion. Activation of the plasminogen cascade, resulting in thedestruction of extracellular matrix for cellular extravasation andmigration, may be a function of tryptase activation of pro-urokinaseplasminogen activator at the P4-P1 sequence of Pro-Arg-Phe-Lys (SEQ IDNO: 4) (Stack, et al., Journal of Biological Chemistry 269 (13):9416-9419 (1994)). Vasoactive intestinal peptide, a neuropeptide that isimplicated in the regulation of vascular permeability, is also cleavedby tryptase, primarily at the Thr-Arg-Leu-Arg (SEQ ID NO: 5) sequence(Tam, et al., Am. J. Respir. Cell Mol. Biol. 3: 27-32 (1990)). TheG-protein coupled receptor PAR-2 can be cleaved and activated bytryptase at the Ser-Lys-Gly-Arg (SEQ ID NO: 6) sequence to drivefibroblast proliferation, whereas the thrombin activated receptor PAR-1is inactivated by tryptase at the Pro-Asn-Asp-Lys (SEQ ID NO: 7)sequence (Molino et al., Journal of Biological Chemistry 272(7):4043-4049 (1997)). Taken together, this evidence suggests a central rolefor tryptase in tissue remodeling as a consequence of disease. This isconsistent with the profound changes observed in several mastcell-mediated disorders. One hallmark of chronic asthma and otherlong-term respiratory diseases is fibrosis and thickening of theunderlying tissues that could be the result of tryptase activation ofits physiological targets. Similarly, a series of reports have shownangiogenesis to be associated with mast cell density, tryptase activityand poor prognosis in a variety of cancers (Coussens et al., Genes andDevelopment 13(11): 1382-97 (1999)); Takanami et al., Cancer 88(12):2686-92 (2000); Toth-Jakatics et al., Human Pathology 31(8): 955-960(2000); Ribatti et al., International Journal of Cancer 85(2): 171-5(2000)).

Methods are known in the art for evaluating whether a particularprotease cleaves a selected peptide sequence. For example, the use of7-amino-4-methyl coumarin (AMC) fluorogenic peptide substrates is awell-established method for the determination of protease specificity(Zimmerman, M., et al., (1977) Analytical Biochemistry 78:47-51).Specific cleavage of the anilide bond liberates the fluorogenic AMCleaving group allowing for the simple determination of cleavage ratesfor individual substrates. More recently, arrays (Lee, D., et al.,(1999) Bioorganic and Medicinal Chemistry Letters 9:1667-72) andpositional-scanning libraries (Rano, T. A., et al., (1997) Chemistry andBiology 4:149-55) of AMC peptide substrate libraries have been employedto rapidly profile the N-terminal specificity of proteases by sampling awide range of substrates in a single experiment. Thus, one of skill inthe art may readily evaluate an array of peptide sequences to determinetheir utility in the present invention without resort to undueexperimentation.

(2) Hydrazine Linkers (H)

In a second embodiment, the conjugate of the invention comprises ahydrazine self-immolative linker, wherein the conjugate has thestructure:X⁴-(L⁴)_(p)-H-(L¹)_(m)-D,wherein D, L¹, L⁴, and X⁴ are as defined above and described furtherherein, and H is a linker comprising the structure:

wherein

-   -   n₁ is an integer from 1-10;    -   n₂ is 0, 1, or 2;    -   each R²⁴ is a member independently selected from the group        consisting of H, substituted alkyl, unsubstituted alkyl,        substituted heteroalkyl, and unsubstituted heteroalkyl; and    -   I is either a bond (i.e., the bond between the carbon of the        backbone and the adjacent nitrogen) or:

-   -   wherein n₃ is 0 or 1, with the proviso that when n₃ is 0, n₂ is        not 0; and    -   n₄ is 1, 2, or 3,    -   wherein when I is a bond, n₁ is 3 and n₂ is 1, D can not be

where R is Me or CH₂—CH₂—NMe₂.

In one embodiment, the substitution on the phenyl ring is a parasubstitution. In preferred embodiments, n₁ is 2, 3, or 4 or n₁ is 3. Inpreferred embodiments, n₂ is 1. In preferred embodiments, I is a bond(i.e., the bond between the carbon of the backbone and the adjacentnitrogen). In one aspect, the hydrazine linker, H, can form a 6-memberedself immolative linker upon cleavage, for example, when n₃ is 0 and n₄is 2. In another aspect, the hydrazine linker, H, can form two5-membered self immolative linkers upon cleavage. In yet other aspects,H forms a 5-membered self immolative linker, H forms a 7-membered selfimmolative linker, or H forms a 5-membered self immolative linker and a6-membered self immolative linker, upon cleavage. The rate of cleavageis affected by the size of the ring formed upon cleavage. Thus,depending upon the rate of cleavage desired, an appropriate size ring tobe formed upon cleavage can be selected.

Five Membered Hydrazine Linkers

In one embodiment, the hydrazine linker comprises a 5-membered hydrazinelinker, wherein H comprises the structure:

In a preferred embodiment, n₁ is 2, 3, or 4. In another preferredembodiment, n₁ is 3. In the above structure, each R²⁴ is a memberindependently selected from the group consisting of H, substitutedalkyl, unsubstituted alkyl, substituted heteroalkyl, and unsubstitutedheteroalkyl. In one embodiment, each R²⁴ is independently H or a C₁-C₆alkyl. In another embodiment, each R²⁴ is independently H or a C₁-C₃alkyl, more preferably H or CH₃. In another embodiment, at least one R²⁴is a methyl group. In another embodiment, each R₂₄ is H. Each R²⁴ isselected to tailor the compounds steric effects and for alteringsolubility.

The 5-membered hydrazine linkers can undergo one or more cyclizationreactions that separate the drug from the linker, and can be described,for example, by:

An exemplary synthetic route for preparing a five membered linker of theinvention is:

The Cbz-protected DMDA b is reacted with 2,2-Dimethyl-malonic acid a insolution with thionyl chloride to form a Cbz-DMDA-2,2-dimethylmalonicacid c. Compound c is reacted with Boc-N-methyl hydrazine d in thepresence of hydrogen to formDMDA-2,2-dimethylmalonic-Boc-N-methylhydrazine e.Six Membered Hydrazine Linkers

In another embodiment, the hydrazine linker comprises a 6-memberedhydrazine linker, wherein H comprises the structure:

In a preferred embodiment, n₁ is 3. In the above structure, each R²⁴ isa member independently selected from the group consisting of H,substituted alkyl, unsubstituted alkyl, substituted heteroalkyl, andunsubstituted heteroalkyl. In one embodiment, each R²⁴ is independentlyH or a C₁-C₆ alkyl. In another embodiment, each R²⁴ is independently Hor a C₁-C₃ alkyl, more preferably H or CH₃. In another embodiment, atleast one R²⁴ is a methyl group. In another embodiment, each R₂₄ is H.Each R²⁴ is selected to tailor the compounds steric effects and foraltering solubility. In a preferred embodiment, H comprises thestructure:

In one embodiment, H comprises a geminal dimethyl substitution. In oneembodiment of the above structure, each R²⁴ independently an H or asubstituted or unsubstituted alkyl.

The 6-membered hydrazine linkers will undergo a cyclization reactionthat separates the drug from the linker, and can be described as:

An exemplary synthetic route for preparing a six membered linker of the

The Cbz-protected dimethyl alanine a in solution with dichlormethane,was reacted with HOAt, and CPI to form a Cbz-protected dimethylalaninehydrazine b. The hydrazine b is deprotected by the action of methanol,forming compound c.

Other Hydrazine Linkers

It is contemplated that the invention comprises a linker having sevenmembers. This linker would likely not cyclize as quickly as the five orsix membered linkers, but this may be preferred for some drug-ligandconjugates. Similarly, the hydrazine linker may comprise two sixmembered rings or a hydrazine linker having one six and one fivemembered cyclization products. A five and seven membered linker as wellas a six and seven membered linker are also contemplated.

Another hydrazine structure, H, has the formula:

-   -   where q is 0, 1, 2, 3, 4, 5, or 6; and    -   each R²⁴ is a member independently selected from the group        consisting of H, substituted alkyl, unsubstituted alkyl,        substituted heteroalkyl, and unsubstituted heteroalkyl. This        hydrazine structure can also form five-, six-, or seven-membered        rings and additional components can be added to form multiple        rings.        (3) Disulfide Linkers (J)

In yet another embodiment, the linker comprises an enzymaticallycleavable disulfide group. In one embodiment, the invention provides acytotoxic drug-ligand compound having a structure according to Formula3:

wherein D, L¹, L⁴, and X⁴ are as defined above and described furtherherein, and J is a disulfide linker comprising a group having thestructure:

wherein

-   -   each R²⁴ is a member independently selected from the group        consisting of H, substituted alkyl, unsubstituted alkyl,        substituted heteroalkyl, and unsubstituted heteroalkyl;    -   each K is a member independently selected from the group        consisting of substituted alkyl, unsubstituted alkyl,        substituted heteroalkyl, unsubstituted heteroalkyl, substituted        aryl, unsubstituted aryl, substituted heteroaryl, unsubstituted        heteroaryl, substituted heterocycloalkyl, unsubstituted        heterocycloalkyl, halogen, NO₂, NR²¹R²², NR²¹COR²², OCONR²¹R²²,        OCOR²¹, and OR²¹

wherein

-   -   R²¹ and R²² are independently selected from the group consisting        of H, substituted alkyl, unsubstituted alkyl, substituted        heteroalkyl, unsubstituted heteroalkyl, substituted aryl,        unsubstituted aryl, substituted heteroaryl, unsubstituted        heteroaryl, substituted heterocycloalkyl and unsubstituted        heterocycloalkyl;    -   a is an integer of 0, 1, 2, 3, or 4; and    -   d is an integer of 0, 1, 2, 3, 4, 5, or 6.

The aromatic ring of the disulfides linker may be substituted with oneor more “K” groups. A “K” group is a substituent on the aromatic ringthat replaces a hydrogen otherwise attached to one of the fournon-substituted carbons that are part of the ring structure. The “K”group may be a single atom, such as a halogen, or may be a multi-atomgroup, such as alkyl, heteroalkyl, amino, nitro, hydroxy, alkoxy,haloalkyl, and cyano. Exemplary K substituents independently include,but are not limited to, F, Cl, Br, I, NO₂, OH, OCH₃, NHCOCH₃, N(CH₃)₂,NHCOCF₃ and methyl. For “Ka”, a is an integer of 0, 1, 2, 3, or 4. In aspecific embodiment, a is 0.

In a preferred embodiment, the linker comprises an enzymaticallycleavable disulfide group of the following formula:

In this embodiment, the identities of L⁴, X⁴, p, and R²⁴ are asdescribed above, and d is 0, 1, 2, 3, 4, 5, or 6. In a particularembodiment, d is 1 or 2.

A more specific disulfide linker is shown in the formula below:

A specific example of this embodiment is as follows:

Preferably, d is 1 or 2.

Another disulfide linker is shown in the formula below:

A specific example of this embodiment is as follows:

Preferably, d is 1 or 2.

In various embodiments, the disulfides are ortho to the amine. Inanother specific embodiment, a is 0. In preferred embodiments, R²⁴ isindependently selected from H and CH₃.

An exemplary synthetic route for preparing a disulfide linker of theinvention is as follows:

A solution of 3-mercaptopropionic acid a is reacted with aldrithiol-2 toform 3-methyl benzothiazolium iodide b. 3-methylbenzothiazolium iodide cis reacted with sodium hydroxide to form compound d. A solution ofcompound d with methanol is further reacted with compound b to formcompound e. Compound e deprotected by the action of acetyl chloride andmethanol forming compound f.

The drug-ligand conjugate of the current invention may optionallycontain two or more linkers. These linkers may be the same or different.For example, a peptidyl linker may be used to connect the drug to theligand and a second peptidyl linker may attach a diagnostic agent thecomplex. Alternatively, any of a peptidyl, hydrazine, or disulfidelinker may connect the drug and ligand complex and any of a peptidyl,hydrazine, or disulfide linker may attach a diagnostic agent to thecomplex. Other uses for additional linkers include linking analyticalagents, biomolecules, targeting agents, and detectable labels to thedrug-ligand complex.

Also within the scope of the present invention are compounds of theinvention that are poly- or multi-valent species, including, forexample, species such as dimers, trimers, tetramers and higher homologsof the compounds of the invention or reactive analogues thereof. Thepoly- and multi-valent species can be assembled from a single species ormore than one species of the invention. For example, a dimeric constructcan be “homo-dimeric” or “heterodimeric.” Moreover, poly- andmulti-valent constructs in which a compound of the invention or areactive analogue thereof, is attached to an oligomeric or polymericframework (e.g., polylysine, dextran, hydroxyethyl starch and the like)are within the scope of the present invention. The framework ispreferably polyfunctional (i.e. having an array of reactive sites forattaching compounds of the invention). Moreover, the framework can bederivatized with a single species of the invention or more than onespecies of the invention.

Moreover, the present invention includes compounds that arefunctionalized to afford compounds having water-solubility that isenhanced relative to analogous compounds that are not similarlyfunctionalized. Thus, any of the substituents set forth herein can bereplaced with analogous radicals that have enhanced water solubility.For example, it is within the scope of the invention to, for example,replace a hydroxyl group with a diol, or an amine with a quaternaryamine, hydroxy amine or similar more water-soluble moiety. In apreferred embodiment, additional water solubility is imparted bysubstitution at a site not essential for the activity towards the ionchannel of the compounds set forth herein with a moiety that enhancesthe water solubility of the parent compounds. Methods of enhancing thewater-solubility of organic compounds are known in the art. Such methodsinclude, but are not limited to, functionalizing an organic nucleus witha permanently charged moiety, e.g., quaternary ammonium, or a group thatis charged at a physiologically relevant pH, e.g. carboxylic acid,amine. Other methods include, appending to the organic nucleus hydroxyl-or amine-containing groups, e.g. alcohols, polyols, polyethers, and thelike. Representative examples include, but are not limited to,polylysine, polyethyleneimine, poly(ethyleneglycol) andpoly(propyleneglycol). Suitable functionalization chemistries andstrategies for these compounds are known in the art. See, for example,Dunn, R. L., et al., Eds. POLYMERIC DRUGS AND DRUG DELIVERY SYSTEMS, ACSSymposium Series Vol. 469, American Chemical Society, Washington, D.C.1991.

Drugs

Drugs, depicted as “D” herein, are provided in the current invention aspart of a drug-ligand conjugate where the drug is linked to a ligandthrough either a peptidyl, hydrazine, or disulfide linker. The drug mustpossess a desired biological activity and contain a reactive functionalgroup in order to link to the ligand. The desired biological activityincludes the diagnosis, cure, mitigation, treatment, or prevention ofdisease in an animal such as a human. Thus, so long as it has the neededreactive functional group, the term “drug” refers to chemicalsrecognized as drugs in the official United States Pharmacopeia, officialHomeopathic Pharmacopeia of the United States, or official NationalFormulary, or any supplement thereof. Exemplary drugs are set forth inthe Physician's Desk Reference (PDR) and in the Orange Book maintainedby the U.S. Food and Drug Administration (FDA). New drugs are beingcontinually being discovered and developed, and the present inventionprovides that these new drugs may also be incorporated into thedrug-ligand complex of the current invention.

Preferred functional groups include primary or secondary amines,hydroxyls, sulfhydryls, carboxyls, aldehydes, and ketones. Morepreferred functional groups include hydroxyls, primary or secondaryamines, sulfhydryls and carboxylic acid functional groups. Even morepreferred functional groups include hydroxyls, primary and secondaryamines and carboxylic acid functional groups. The drug must have atleast one, but may have 2, 3, 4, 5, 6 or more reactive functionalgroups. Additionally, a self-immolative spacer, L¹, may be incorporatedbetween the reactive functional group of the drug and the peptide,hydrazine or disulfide linker.

The drug-ligand conjugate is effective for the usual purposes for whichthe corresponding drugs are effective, but have superior efficacybecause of the ability, inherent in the ligand, to transport the drug tothe desired cell where it is of particular benefit.

Exemplary drugs include proteins, peptides, and small molecule drugscontaining a functional group for linkage to the ligand. Morespecifically, these drugs include, for example, the enzyme inhibitorssuch as dihydrofolate reductase inhibitors, and thymidylate synthaseinhibitors, DNA intercalators, DNA cleavers, topoisomerase inhibitors,the anthracycline family of drugs, the vinca drugs, the mitomycins, thebleomycins, the cytotoxic nucleosides, the pteridine family of drugs,diynenes, the podophyllotoxins, differentiation inducers, and taxols.

Preferred drugs of the current invention include cytotoxic drugs usefulin cancer therapy and other small molecules, proteins or polypeptideswith desired biological activity, such as a toxin. The drug may beselected to be activated at a tumor cells by conjugation to atumor-specific ligand. These tumor specific drug-ligand conjugates havetumor specificity arising from the specificity of the ligand. Examplesof this are drug-ligand conjugates that are highly selective substratesfor tumor specific enzymes, where these enzymes are present in theproximity of the tumor in sufficient amounts to generate cytotoxiclevels of free drug in the vicinity of the tumor. One advantage of thesetumor-specific drug-ligand complexes is that they are stable toadventitious proteases in the human serum. Another advantage of thedrug-ligand complex is that they are less toxic than the correspondingfree drug; additionally, the specificity of the complex may allow forlower overall concentrations to be used relative to the free drug sincethe increased specificity will result in a higher percentage of thecomplex to be present at the tumor site.

Cytotoxins

Cytotoxic drugs useful in the current invention include, for example,duocarmycins and CC-1065, and analogues thereof, including CBI(1,2,9,9a-tetrahydrocyclopropa[c]benz[e]indol-4-one)-based analogues,MCBI(7-methoxy-1,2,9,9a-tetra-hydrocyclopropa[c]benz[e]indol-4-one)-basedanalogues and CCBI(7-cyano-1,2,9,9a-tetra-hydrocyclo-propa[c]benz[e]-indol-4-one)-basedanalogues of the duocarmycins and CC-1065, doxorubicin and doxorubicinconjugates such as morpholino-doxorubicin andcyanomorpholino-doxorubicin, dolastatins such as dolestatin-10,combretastatin, calicheamicin, maytansine, maytansine analogs, DM-1,auristatin E, auristatin EB (AEB), auristatin EFP (AEFP), monomethylauristatin E (MMAE), 5-benzoylvaleric acid-AE ester (AEVB), tubulysins,disorazole, epothilones, Paclitaxel, docetaxel, SN-38, Topotecan,rhizoxin, echinomycin, colchicine, vinblastin, vindesine, estramustine,cemadotin, eleutherobin, methotrexate, methopterin,dichloromethotrexate, 5-fluorouracil, 6-mercaptopurine, cytosinearabinoside, melphalan, leurosine, leurosideine, actinomycin,daunorubicin and daunorubicin conjugates, mitomycin C, mitomycin A,caminomycin, aminopterin, tallysomycin, podophyllotoxin andpodophyllotoxin derivatives such as etoposide or etoposide phosphate,vincristine, taxol, taxotere retinoic acid, butyric acid, N⁸-acetylspermidine, camptothecin, and their analogues. Other known drugs may bemodified in order to provide a functional group for conjugation to thelinker described herein. Such chemical modification is known in the art.

Preferred cytotoxins for use in the current invention include:duocarmycins and CC-1065, and CCBI-based and MCBI-based analoguesthereof, morpholino-doxorubicin, cyanomorpholino-doxorubicin,dolastatin-10, combretastatin, calicheamicin, maytansine, DM-1,auristatin E, AEB, AEFP, MMAE, Tubulysin A, Disorazole, epothilone A andepothilone B.

Particularly preferred cytotoxins of the present invention are active,potent duocarmycin derivatives and CC-1065. The parent agents areexceptionally potent antitumor antibiotics that derive their biologicaleffects through the reversible, stereoelectronically controlled sequenceselective alkylation of DNA (Boger et al. J. Org. Chem. 55: 4499 (1990);Boger et al. J. Am. Chem. Soc. 112: 8961 (1990); Boger et al., J. Am.Chem. Soc. 113: 6645 (1991); Boger et al. J. Am. Chem. Soc. 115: 9872(1993); Boger et al., Bioorg. Med. Chem. Lett. 2: 759 (1992)).Subsequent to the initial disclosure of the duocarmycins, extensiveefforts have been devoted to elucidating the DNA alkylation selectivityof the duocarmycins and its structural origin.

A particularly preferred aspect of the current invention provides acytotoxic compound having a structure according to Formula 7:

in which ring system A is a member selected from substituted orunsubstituted aryl substituted or unsubstituted heteroaryl andsubstituted or unsubstituted heterocycloalkyl groups. Exemplary ringsystems include phenyl and pyrrole.

The symbols E and G are independently selected from H, substituted orunsubstituted alkyl, substituted or unsubstituted heteroalkyl, aheteroatom, a single bond or E and G are optionally joined to form aring system selected from substituted or unsubstituted aryl, substitutedor unsubstituted heteroaryl and substituted or unsubstitutedheterocycloalkyl.

The symbol X represents a member selected from O, S and NR²³. R²³ is amember selected from H, substituted or unsubstituted alkyl, substitutedor unsubstituted heteroalkyl, and acyl.

The symbol R³ represents a member selected from (═O), SR¹¹, NHR¹¹ andOR¹¹, in which R¹¹ is H, substituted or unsubstituted alkyl, substitutedor unsubstituted heteroalkyl, diphosphates, triphosphates, acyl,C(O)R¹²R¹³, C(O)OR¹², C(O)NR¹²R¹³, P(O)(OR¹²)₂, C(O)CHR¹²R¹³, SR¹² orSiR¹²R¹³R¹⁴. The symbols R'², R¹³, and R¹⁴ independently represent H,substituted or unsubstituted alkyl, substituted or unsubstitutedheteroalkyl and substituted or unsubstituted aryl, wherein R¹² and R¹³together with the nitrogen or carbon atom to which they are attached areoptionally joined to form a substituted or unsubstitutedheterocycloalkyl ring system having from 4 to 6 members, optionallycontaining two or more heteroatoms. One or more of R¹², R¹³, or R¹⁴ caninclude a cleaveable group within its structure.

R⁴, R⁴′, R⁵ and R⁵′ are members independently selected from H,substituted or unsubstituted alkyl, substituted or unsubstituted aryl,substituted or unsubstituted heteroaryl, substituted or unsubstitutedheterocycloalkyl, halogen, NO₂, NR¹⁵R¹⁶, NC(O)R¹⁵, OC(O)NR¹⁵R¹⁶,OC(O)OR¹⁵, C(O)R¹⁵, SR¹⁵, OR¹⁵, CR¹⁵═NR¹⁶, and O(CH₂)_(n)N(CH₃)₂,wherein n is an integer from 1 to 20. R¹⁵ and R¹⁶ independentlyrepresent H, substituted or unsubstituted alkyl, substituted orunsubstituted heteroalkyl, substituted or unsubstituted aryl,substituted or unsubstituted heteroaryl, substituted or unsubstitutedheterocycloalkyl and substituted or unsubstituted peptidyl, wherein R¹⁵and R¹⁶ together with the nitrogen atom to which they are attached areoptionally joined to form a substituted or unsubstitutedheterocycloalkyl ring system having from 4 to 6 members, optionallycontaining two or more heteroatoms. One exemplarly structure is aniline.

R⁴, R^(4′), R⁵, R^(5′), R¹¹, R¹², R¹³, R¹⁵ and R¹⁶ optionally containone or more cleaveable groups within their structure. Exemplarycleaveable groups include, but are not limited to peptides, amino acids,hydrazines, and disulfides.

At least one of R¹¹, R¹², R¹³, R¹⁵ and R¹⁶ is used to join the drug to alinker of the present invention, as described herein, for example to L¹,if present or to F, H, or J.

In a still further exemplary embodiment, at least one of R⁴, R^(4′), R⁵,R⁵′, R¹¹, R¹², R¹³, R¹⁵ and R¹⁶ bears a reactive group appropriate forconjugating the compound. In a further exemplary embodiment, R⁴, R^(4′),R⁵, R⁵′, R¹¹, R¹², R¹³, R¹⁵ and R¹⁶ are independently selected from H,substituted alkyl and substituted heteroalkyl and have a reactivefunctional group at the free terminus of the alkyl or heteroalkylmoiety. One or more of R⁴, R⁴′, R⁵, R⁵′, R¹¹, R¹², R¹³, R¹⁵ and R¹⁶ maybe conjugated to another species, e.g., targeting agent, detectablelabel, solid support, etc.

As will be apparent from the discussion herein, when at least one of R¹⁵and R¹⁶ comprises a reactive functional group, that group can be acomponent of a bond between the drug and another molecule. In anexemplary embodiment in which at least one of R¹⁵ and R¹⁶ comprises alinkage between the drug and another species, at least one of R¹⁵ andR¹⁶ is a moiety that is cleaved by an enzyme.

In a further exemplary embodiment, at least one of R⁴, R⁴′, R⁵ and R⁵′is:

In Formula 8, the symbols X² and Z¹ represent members independentlyselected from O, S and NR²³. The groups R¹⁷ and R¹⁸ are independentlyselected from H, substituted or unsubstituted alkyl, substituted orunsubstituted heteroalkyl, substituted or unsubstituted aryl,substituted or unsubstituted heteroaryl, substituted or unsubstitutedheterocycloalkyl, halogen, NO₂, NR¹⁹R²⁰, NC(O)R¹⁹, OC(O)NR¹⁹, OC(O)OR¹⁹,C(O)R¹⁹, SR¹⁹ or OR¹⁹, with the proviso that at least one one of R¹²,R¹³, R¹⁹, or R²⁰ comprises a linker of the present invention, asdisclosed herein.

The symbols R¹⁹ and R²⁰ independently represent substituted orunsubstituted alkyl, substituted or unsubstituted heteroalkyl,substituted or unsubstituted aryl, substituted or unsubstitutedheteroaryl, substituted or unsubstituted heterocycloalkyl, substitutedor unsubstituted peptidyl, wherein R¹⁹ and R²⁰ together with thenitrogen atom to which they are attached are optionally joined to form asubstituted or unsubstituted heterocycloalkyl ring system having from 4to 6 members, optionally containing two or more heteroatoms, with theproviso that when Z¹ is NH, both R¹⁷ and R¹⁸ are not H, and R¹⁷ is notNH₂. Throughout the present specification, the symbols R¹⁹ and R²⁰ alsoencompass the groups set forth for R⁴ and R⁵. Thus, for example, it iswithin the scope of the present invention to provide compounds havingtwo or more of the fused phenyl-heterocyclic ring systems set forthimmediately above linked in series, or a fused ring in combination witha linker. Moreover, in those embodiments in which a linker is present,the linker may be present as an R⁴, R⁴′, R⁵, or R⁵′ substituent or as anR¹⁷ or R¹⁸ substituent.

R⁶ is a single bond which is either present or absent. When R⁶ ispresent, R⁶ and R⁷ are joined to form a cyclopropyl ring. R⁷ is CH₂—X¹or CH₂—. When R⁷ is CH₂— it is a component of the cyclopropane ring. Thesymbol X¹ represents a leaving group such as a halogen, for example Cl,Br or F. The combinations of R⁶ and R⁷ are interpreted in a manner thatdoes not violate the principles of chemical valence.

The curved line within the six-membered ring indicates that the ring mayhave one or more degree of unsaturation, and it may be aromatic. Thus,ring structures such as those set forth below, and related structures,are within the scope of Formula (9):

In an exemplary embodiment, ring system A is a substituted orunsubstituted phenyl ring. Ring system A is preferably substituted withone or more aryl group substituents as set forth in the definitionssection herein. In one preferred embodiment, the phenyl ring issubstituted with a CN or methoxy moiety.

In another exemplary embodiment, the invention provides a compoundhaving a structure according to Formula 10:

In this embodiment, the identities of the radicals R³, R⁴, R⁴′, R⁵, R⁵′,R₆, R⁷ and X are substantially as described above. The symbol Z is amember independently selected from O, S and NR²³. The symbol R²³represents a member selected from H, substituted or unsubstituted alkyl,substituted or unsubstituted heteroalkyl, and acyl. Each R²³ isindependently selected. The symbol R¹ represents H, substituted orunsubstituted lower alkyl, or C(O)R⁸ or CO₂R⁸. R⁸ is a member selectedfrom substituted alkyl, unsubstituted alkyl, NR⁹R¹⁰, NR⁹NHR¹⁰ and OR⁹.R⁹, and R¹⁰ are independently selected from H, substituted orunsubstituted alkyl and substituted or unsubstituted heteroalkyl. Theradical R² is H, or substituted or unsubstituted lower alkyl. It isgenerally preferred that when R² is substituted alkyl, it is other thana perfluoroalkyl, e.g., CF₃. In one embodiment, R² is a substitutedalkyl wherein the substitution is not a halogen. In another embodiment,R² is an unsubstituted alkyl.

As discussed above, X¹ may be a leaving group. Useful leaving groupsinclude, but are not limited to, halogens, azides, sulfonic esters(e.g., alkylsulfonyl, arylsulfonyl), oxonium ions, alkyl perchlorates,ammonioalkanesulfonate esters, alkylfluorosulfonates and fluorinatedcompounds (e.g., triflates, nonaflates, tresylates) and the like.Particular halogens useful as leaving groups are F, Cl and Br. Thechoice of these and other leaving groups appropriate for a particularset of reaction conditions is within the abilities of those of skill inthe art (see, for example, March J, ADVANCED ORGANIC CHEMISTRY, 2ndEdition, John Wiley and Sons, 1992; Sandler S R, Karo W, ORGANICFUNCTIONAL GROUP PREPARATIONS, 2nd Edition, Academic Press, Inc., 1983;and Wade L G, COMPENDIUM OF ORGANIC SYNTHETIC METHODS, John Wiley andSons, 1980).

In an exemplary embodiment R¹ is an ester moiety, such as CO₂CH₃. In afurther exemplary embodiment, R² is a lower alkyl group, which may besubstituted or unsubstituted. A presently preferred lower alkyl group isCH₃. In a still further embodiment, R¹ is CO₂CH₃, and R² is CH₃.

In yet another exemplary embodiment, R⁴, R⁴′, R⁵, and R⁵′ are membersindependently selected from H, halogen, NH₂, OMe, O(CH₂)₂N(Me)₂ and NO₂.

In one embodiment, the drug is selected such that the leaving group X¹is a member selected from the group consisting of halogen,alkylsulfonyl, arylsulfonyl, and azide. In another embodiment, Z is O.In certain embodiments, R¹ may be CO₂CH₃ or R² may be CH₃; additionally,R¹ may be CO₂CH₃, and R² may be CH₃. One of R⁴, R⁴′, R⁵ or R⁵′ may beC(O)R¹⁵ and the other three of R⁴, R⁴′, R⁵ and R⁵′ are H. Additionally,at least one of R⁴, R⁴′, R⁵ and R⁵′ may be other than a member selectedfrom H and OCH₃. In one embodiment, R⁴, R⁴′, R⁵ and R⁵′ are membersindependently selected from H, halogen, NH₂, O(CH₂)₂N(Me)₂ and NO₂.

In a preferred embodiment, one of R⁴, R⁴′, R⁵ or R⁵′ is O(CH₂)₂N(Me)₂and the others of R⁴, R⁴′, R⁵ and R⁵′ are H. In another embodiment, R⁷is CH₂—X¹ where X¹ is F, Cl or Br and R⁶ is absent.

In yet another exemplary embodiment, the invention provides compoundshaving a structure according to Formula 11 and 12:

In one embodiment of the Formula above, X is preferably O; and Z ispreferably O. In another embodiment, Z is NR²³ or O. Alternatively, oneof R⁴, R⁴′, R⁵ or R⁵′ may be O(CH₂)₂N(Me)₂ while the other three of R⁴,R⁴′, R⁵ or R⁵′ are H. In one embodiment, R⁴, R⁴′, R⁵ or R⁵′ may beselected from the group consisting of R²⁹, COOR²⁹, C(O)NR²⁹, andC(O)NNR²⁹, wherein R²⁹ is selected from the group consisting of H, OH,substituted alkyl, unsubstituted alkyl, substituted cycloalkyl,unsubstituted cycloalkyl, substituted heteroalkyl, unsubstitutedheteroalkyl, substituted cycloheteroalkyl, unsubstitutedcycloheteroalkyl, substituted heteroaryl, and unsubstituted heteroaryl.

In another embodiment of the Formula above X is preferably O, Z ispreferably O, R₁ is preferably CO₂CH₃, R₇ is preferably CH₂—Cl, R₂ ispreferably CH₃, R₃ is preferably OH. Alternatively, one of R⁴, R⁴′, R⁵or R⁵′ may be NHC(O)(C₆H₄)NH₂ while the other three of R⁴, R⁴′, R⁵ orR⁵′ are H.

In one embodiment, R²⁹ may be selected from the group consisting of:

In yet another embodiment of the drug, one member selected from R⁴ andR⁵ is:

wherein X² and Z¹ are members independently selected from O, S and NR²³;R¹⁷ and R¹⁸ are members independently selected from the group consistingof H, substituted or unsubstituted alkyl, substituted or unsubstitutedheteroalkyl, substituted or unsubstituted aryl, substituted orunsubstituted heteroaryl, substituted or unsubstituted heterocycloalkyl,halogen, NO₂, NR¹⁹R²⁰, NC(O)R¹⁹, OC(O)NR¹⁹, OC(O)OR¹⁹, C(O)R¹⁹, OR¹⁹,and O(CH₂)_(n)N(CH₃)₂. In this embodiment, n is an integer from 1 to 20;R¹⁹ and R²⁰ are independently selected from substituted or unsubstitutedalkyl, substituted or unsubstituted heteroalkyl, substituted orunsubstituted aryl, substituted or unsubstituted heteroaryl, andsubstituted or unsubstituted heterocycloalkyl, wherein R¹⁹ and R²⁰together with the nitrogen atom to which they are attached areoptionally joined to form a substituted or unsubstitutedheterocycloalkyl ring system having from 4 to 6 members, optionallycontaining two or more heteroatoms, wherein one of R¹¹, R¹², R¹³, R¹⁵,R¹⁶, R¹⁹, or R²⁰ links said drug to L¹, if present, or to F. In onepreferred embodiment, X² is O and Z¹ is O or NR²³.

Another preferred structure of the duocarmycin analog of Formula 7 is astructure in which the ring system A is an unsubstituted or substitutedphenyl ring. The preferred substituents on the drug molecule describedhereinabove for the structure of Formula 7 when the ring system A is apyrrole are also preferred substituents when the ring system A is anunsubstituted or substituted phenyl ring.

For example, in a preferred embodiment, the drug (D) comprises astructure:

In this structure, R³, R⁶, R⁷, X are as described above for Formula 7.Furthermore, Z is a member selected from O, S and NR²³, wherein R²³ is amember selected from H, substituted or unsubstituted alkyl, substitutedor unsubstituted heteroalkyl, and acyl;

R¹ is H, substituted or unsubstituted lower alkyl, C(O)R⁸, or CO₂R⁸,wherein R⁸ is a member selected from NR⁹R¹⁰ and OR⁹, in which R⁹ and R¹⁰are members independently selected from H, substituted or unsubstitutedalkyl and substituted or unsubstituted heteroalkyl;

R^(1′) is H, substituted or unsubstituted lower alkyl, or C(O)R⁸,wherein R⁸ is a member selected from NR⁹R¹⁰ and OR⁹, in which R⁹ and R¹⁰are members independently selected from H, substituted or unsubstitutedalkyl and substituted or unsubstituted heteroalkyl;

R² is H, or substituted or unsubstituted lower alkyl or unsubstitutedheteroalkyl or cyano or alkoxy; and R²′ is H, or substituted orunsubstituted lower alkyl or unsubstituted heteroalkyl.

At least one of R¹¹, R¹², R¹³, R¹⁵ or R¹⁶ links the drug to L¹, ifpresent, or to F, H, or J.

In a preferred embodiment, one of R⁴, R⁴′, R⁵ or R⁵′ is O(CH₂)₂N(Me)₂and the others of R⁴, R⁴′, R⁵ and R⁵′ are H. In another embodiment, R⁷is CH₂—X¹ where X¹ is F, Cl or Br and R⁶ is absent.

In one embodiment, the invention provides a cytotoxic drug-ligandcompound having a structure according to the following formula:

wherein the symbol L¹ represents a self-immolative spacer where m is aninteger of 0, 1, 2, 3, 4, 5, or 6.

The symbol X⁴ represents a member selected from the group consisting ofprotected reactive functional groups, unprotected reactive functionalgroups, detectable labels, and targeting agents.

The symbol L⁴ represents a linker member, and p is 0 or 1. L⁴ is amoiety that imparts increased solubility or decreased aggregationproperties to the conjugates. Examples of L⁴ moieties includesubstituted alkyl, unsubstituted alkyl, substituted aryl, unsubstitutedaryl, substituted heteroalkyl, or unsubstituted heteroalkyl, any ofwhich may be straight, branched, or cyclic, a positively or negativelycharged amino acid polymer, such as polylysine or polyargenine, or otherpolymers such as polyethylene glycol.

The symbol Q represent any cleavable linker including, but not limitedto, any of the peptidyl, hydrozone, and disulfide linkers describedherein. Other suitable linkers include, but are not limited to, thosedescribed in U.S. Pat. No. 6,214,345; U.S. Patent ApplicationsPublication Nos. 2003/0096743, 2003/0130189, and 2004/121940; PCT PatentApplications Publication Nos. WO 03/026577 and WO 04/043493; andEuropean Patent Applications Publication Nos. EP1243276 and EP1370298,all of which are incorporated herein by reference. Cleavable linkersinclude those that can be selectively cleaved by a chemical orbiological process and upon cleavage separate the drug, D¹, from X⁴.Cleavage can occur anywhere along the length of the linker or at eitherterminus of the linker.

The symbol D¹ represents a drug having the following formula:

-   -   wherein X and Z are members independently selected from O, S and        NR²³;    -   R²³ is a member selected from H, substituted or unsubstituted        alkyl, substituted or unsubstituted heteroalkyl, and acyl;    -   R¹ is H, substituted or unsubstituted lower alkyl, C(O)R⁸, or        CO₂R⁸,    -   R¹′ is H, substituted or unsubstituted lower alkyl, or C(O)R⁸,    -   wherein R⁸ is a member selected from NR⁹R¹⁰ and OR⁹ and R⁹ and        R¹⁰ are members independently selected from H, substituted or        unsubstituted alkyl and substituted or unsubstituted        heteroalkyl;    -   R² is H, or substituted or unsubstituted lower alkyl or        unsubstituted heteroalkyl or cyano or alkoxy;    -   R²′ is H, or substituted or unsubstituted lower alkyl or        unsubstituted heteroalkyl,    -   R³ is a member selected from the group consisting of SR¹¹, NHR¹¹        and OR¹¹, wherein R¹¹ is a member selected from the group        consisting of H, substituted alkyl, unsubstituted alkyl,        substituted heteroalkyl, unsubstituted heteroalkyl,        diphosphates, triphosphates, acyl, C(O)R¹²R¹³, C(O)OR¹²,        C(O)NR¹²R¹³, P(O)(OR¹²)₂C(O)CHR¹²R¹³, SR¹² and SiR¹²R¹³R¹⁴, in        which R¹², R¹³, and R¹⁴ are members independently selected from        H, substituted or unsubstituted alkyl, substituted or        unsubstituted heteroalkyl and substituted or unsubstituted aryl,        wherein R¹² and R¹³ together with the nitrogen or carbon atom to        which they are attached are optionally joined to form a        substituted or unsubstituted heterocycloalkyl ring system having        from 4 to 6 members, optionally containing two or more        heteroatoms;    -   wherein at least one of R¹¹, R¹², and R¹³ links said drug to L',        if present, or to Q,    -   R⁶ is a single bond which is either present or absent and when        present R⁶ and R⁷ are joined to form a cyclopropyl ring; and    -   R⁷ is CH₂—X¹ or CH₂— joined in said cyclopropyl ring with R⁶,        wherein    -   X¹ is a leaving group,    -   R⁴, R⁴′, R⁵, and R⁵′ are members independently selected from the        group consisting of H, substituted alkyl, unsubstituted alkyl,        substituted aryl, unsubstituted aryl, substituted heteroaryl,        unsubstituted heteroaryl, substituted heterocycloalkyl,        unsubstituted heterocycloalkyl, halogen, NO₂, NR¹⁵R¹⁶, NC(O)R¹⁵,        OC(O)NR¹⁵R¹⁶, OC(O)OR¹⁵, C(O)R¹⁵, SR¹⁵, OR¹⁵, CR¹⁵═NR¹⁶, and        O(CH₂)NR²⁴R²⁵ wherein n is an integer from 1 to 20;    -   R¹⁵ and R¹⁶ are independently selected from H, substituted or        unsubstituted alkyl, substituted or unsubstituted heteroalkyl,        substituted or unsubstituted aryl, substituted or unsubstituted        heteroaryl, substituted or unsubstituted heterocycloalkyl, and        substituted or unsubstituted peptidyl, wherein R¹⁵ and R¹⁶        together with the nitrogen atom to which they are attached are        optionally joined to form a substituted or unsubstituted        heterocycloalkyl ring system having from 4 to 6 members,        optionally containing two or more heteroatoms;    -   and R²⁴ and R²⁵ are independently selected from unsubstituted        alkyl, and    -   wherein at least one of R⁴, R⁴′, R⁵ and R⁵′ is        O(CH₂)_(n)NR²⁴R²⁵.

In some embodiments, n is 2. In some embodiments, R²⁴ and R²⁵ aremethyl. In some embodiments, R⁴ is O(CH₂)_(n)NR²⁴R²⁵ and R⁴′, R⁵ and R⁵′are H. In some embodiments, R⁴ is O(CH₂)₂N(CH₃)₂ and R⁴′, R⁵ and R⁵′ areH. In some embodiment, Q is a linker selected from F, H, and J, asdescribed above. In some embodiments, R¹, R¹′, R², and R²′ are H.

A preferred formula for drug, D¹, is the following:

Another preferred embodiment of drug D¹ is the following:

Yet additional preferred embodiments of drug D¹ are the following:

In another exemplary embodiment of the current invention, the cytotoxicdrug may by a tubulysin analog or related compound, such as thecompounds described by the structure according to Formula 13:

where R₁ and R₂ are H or a lower alkyl, or are more particularlyisobutyl, ethyl, propyl, or t-butyl and R₃ is H or OH. Tubulysin and itsuse in treating cancer has been described in, for example, PCTPublications WO 2004/005327 and WO 2004/005326. The production oftubulysin compounds is described in DE10008089. Methods that may be usedto link the tubulysin to various linkers of the current invention areprovided in the examples. Preferred tubulysin analogs are Tubulysin A-F.

Preferred Duocarmycin and CBI Conjugates

The peptide, hydrazine or disulfide linkers of the invention can be usedin conjugates containing duocarmycin or CBI analogs as cytotoxic agents.Preferred conjugates of the invention are described in further detailbelow. Unless otherwise indicated, substituents are defined as set forthabove in the sections regarding cytotoxins, peptide linkers, hydrazinelinkers and disulfide linkers.

A. Peptide Linker Conjugates

In a preferred embodiment, the invention provides a peptide linkerconjugate having the structure:

-   -   wherein X¹ is a halogen;    -   X is a member selected from O, S and NR²³;    -   R²³ is a member selected from H, substituted or unsubstituted        alkyl, substituted or unsubstituted heteroalkyl, and acyl; and    -   R⁴, R⁴′, R⁵ and R⁵′ are members independently selected from the        group consisting of H, substituted alkyl, unsubstituted alkyl,        substituted aryl, unsubstituted aryl, substituted heteroaryl,        unsubstituted heteroaryl, substituted heterocycloalkyl,        unsubstituted heterocycloalkyl, halogen, NO₂, NR¹⁵R¹⁶, NC(O)R¹⁵,        OC(O)NR¹⁵R¹⁶, OC(O)OR¹⁵, C(O)R¹⁵, OR¹⁵, and O(CH₂)_(n)N(CH₃)₂

wherein

-   -   n is an integer from 1 to 20; and    -   R¹⁵ and R¹⁶ are independently selected from H, substituted or        unsubstituted alkyl, substituted or unsubstituted heteroalkyl,        substituted or unsubstituted aryl, substituted or unsubstituted        heteroaryl, and substituted or unsubstituted, wherein R¹⁵ and        R¹⁶ together with the nitrogen atom to which they are attached        are optionally joined to form a substituted or unsubstituted        heterocycloalkyl ring system having from 4 to 6 members,        optionally containing two or more heteroatoms.

Non-limiting examples of such conjugates include the followingstructures:

wherein X¹ is Cl or Br;and wherein Ab is an antibody, or fragment thereof.

In another preferred embodiment, the invention provides a conjugatehaving the structure:

wherein X¹ is a leaving group;

Z and X are members independently selected from O, S and NR²³,

-   -   wherein R²³ is a member selected from H, substituted or        unsubstituted alkyl, substituted or unsubstituted heteroalkyl,        and acyl; and

R³ is selected from the group consisting of H, substituted alkyl,unsubstituted alkyl, substituted aryl, unsubstituted aryl, substitutedheteroaryl, unsubstituted heteroaryl, substituted heterocycloalkyl,unsubstituted heterocycloalkyl, halogen, NO₂, NR¹⁵R¹⁶, NC(O)R¹⁵,OC(O)NR¹⁵R¹⁶, OC(O)OR¹⁵, C(O)R¹⁵, OR¹⁵, and O(CH₂)_(n)N(CH₃)₂

-   -   wherein        -   n is an integer from 1 to 20;        -   R¹⁵ and R¹⁶ are independently selected from H, substituted            or unsubstituted alkyl, substituted or unsubstituted            heteroalkyl, substituted or unsubstituted aryl, substituted            or unsubstituted heteroaryl, and substituted or            unsubstituted, wherein R¹⁵ and R¹⁶ together with the            nitrogen atom to which they are attached are optionally            joined to form a substituted or unsubstituted            heterocycloalkyl ring system having from 4 to 6 members,            optionally containing two or more heteroatoms.

Non-limiting examples of such conjugates include the followingstructures:

wherein each b is independently an integer from 0 to 20, and Ab is anantibody, or fragment thereof.

In yet other preferred embodiments, the invention provides a peptidelinker conjugate selected from the following structures:

wherein X¹ is Cl or Br, and Ab is an antibody, or fragment thereof.

In still other embodiments, the invention provides a peptide linkerconjugate selected from the following structures:

wherein X¹ is Cl or Br, and Ab is an antibody, or fragment thereof.

In still other embodiments, the invention provides a peptide linkerconjugate having the following structure:

wherein X¹ is Cl or Br, and Ab is an antibody or fragment thereof.

B. Hydrazine Linker Conjugates

In a preferred embodiment, the invention provides a hydrazine linkerconjugate having the structure:

In another preferred embodiment, the invention provides a hydrazinelinker conjugate having the structure:

In yet other preferred embodiments, the invention provides a hydrazinelinker conjugate having structure selected from:

wherein PEG is a polyethylene glycol moiety and X¹ is Cl or Br.

In still other preferred embodiments, the invention provides a hydrazinelinker conjugate selected from the following structures:

wherein X¹ is Cl or Br, and Ab is an antibody, or fragment thereof.

In yet another preferred embodiment, there is a hydrazine linkerconjugate selected from the following structures:

C. Disulfide Linker Conjugates

In a preferred embodiment, the invention provides a disulfide linkerconjugate having the structure:

Non-limiting examples of such structures include the following:

wherein X¹ is Cl or Br, and Ab is an antibody, or fragment thereof.Ligands

The ligands of the current invention are depicted as “X⁴”. In thisinvention, X⁴ represents a member selected from the group consisting ofprotected reactive functional groups, unprotected reactive functionalgroups, detectable labels, and targeting agents. Preferred ligands aretargeting agents, such as antibodies and fragments thereof.

In a preferred embodiment, the group X⁴ can be described as a memberselected from R²⁹, COOR²⁹, C(O)NR²⁹, and C(O)NNR²⁹ wherein R²⁹ is amember selected from substituted or unsubstituted alkyl, substituted orunsubstituted heteroalkyl and substituted or unsubstituted heteroaryl.In yet another exemplary embodiment, R²⁹ is a member selected from H;OH; NHNH₂;

-   -   wherein R³⁰ represents substituted or unsubstituted alkyl        terminated with a reactive functional group, substituted or        unsubstituted heteroaryl terminated with a functional group. The        above structures act as reactive protective groups that can be        reacted with, for example, a side chain of an amino acid of a        targeting agent, such as an antibody, to thereby link the        targeting agent to the linker-drug moiety.        Targeting Agents

The linker arms and cytotoxins of the invention can be linked totargeting agents that selectively deliver a payload to a cell, organ orregion of the body. Exemplary targeting agents such as antibodies (e.g.,chimeric, humanized and human), ligands for receptors, lectins,saccharides, antibodies, and the like are recognized in the art and areuseful without limitation in practicing the present invention. Othertargeting agents include a class of compounds that do not includespecific molecular recognition motifs include macromolecules such aspoly(ethylene glycol), polysaccharide, polyamino acids and the like,which add molecular mass to the cytotoxin. The additional molecular massaffects the pharmacokinetics of the cytotoxin, e.g., serum half-life.

In an exemplary embodiment, the invention provides a cytotoxin, linkeror cytotoxin-linker conjugate with a targeting agent that is abiomolecule, e.g., an antibody, receptor, peptide, lectin, saccharide,nucleic acid or a combination thereof. Routes to exemplary conjugates ofthe invention are set forth in the Schemes above.

Biomolecules useful in practicing the present invention can be derivedfrom any source. The biomolecules can be isolated from natural sourcesor can be produced by synthetic methods. Proteins can be naturalproteins or mutated proteins. Mutations can be effected by chemicalmutagenesis, site-directed mutagenesis or other means of inducingmutations known to those of skill in the art. Proteins useful inpracticing the instant invention include, for example, enzymes,antigens, antibodies and receptors. Antibodies can be either polyclonalor monoclonal, but most preferably are monoclonal. Peptides and nucleicacids can be isolated from natural sources or can be wholly or partiallysynthetic in origin.

In a preferred embodiment, the targeting agent is an antibody, orantibody fragment, that is selected based on its specificity for anantigen expressed on a target cell, or at a target site, of interest. Awide variety of tumor-specific or other disease-specific antigens havebeen identified and antibodies to those antigens have been used orproposed for use in the treatment of such tumors or other diseases. Theantibodies that are known in the art can be used in the conjugates ofthe invention, in particular for the treatment of the disease with whichthe target antigen is associated. Non-limiting examples of targetantigens (and their associated diseases) to which anantibody-linker-drug conjugate of the invention can be targeted include:Her2 (breast cancer), CD20 (lymphomas), EGFR (solid tumors), CD22(lymphomas, including non-Hodgkin's lymphoma), CD52 (chronic lymphocyticleukemia), CD33 (acute myelogenous leukemia), CD4 (lymphomas, autoimmunediseases, including rheumatoid arthritis), CD30 (lymphomas, includingnon-Hodgkin's lymphoma), Muc18 (melanoma), integrins (solid tumors),PSMA (prostate cancer, benign prostatic hyperplasia), CEA (colorectalcancer), CD11a (psoriasis), CD80 (psoriasis), CD23 (asthma), CD40L(immune thromobcytopenic purpura), CTLA4 (T cell lymphomas) and BLys(autoimmune diseases, including systemic lupus erythematosus).

In those embodiments wherein the recognition moiety is a protein orantibody, the protein can be tethered to a surface or a self assembledmonolayer (SAM) component or connected through a spacer arm by anyreactive peptide residue available on the surface of the protein. Inpreferred embodiments, the reactive groups are amines or carboxylates.In particularly preferred embodiments, the reactive groups are theε-amine groups of lysine residues. Furthermore, these molecules can beadsorbed onto the surface of the substrate or SAM by non-specificinteractions (e.g., chemisorption, physisorption).

Recognition moieties which are antibodies can be used to recognizeanalytes which are proteins, peptides, nucleic acids, saccharides orsmall molecules such as drugs, herbicides, pesticides, industrialchemicals and agents of war. Methods of raising antibodies for specificmolecules are well-known to those of skill in the art. See, U.S. Pat.No. 5,147,786, issued to Feng et al. on Sep. 15, 1992; U.S. Pat. No.5,334,528, issued to Stanker et al. on Aug. 2, 1994; U.S. Pat. No.5,686,237, issued to Al-Bayati, M. A. S. on Nov. 11, 1997; and U.S. Pat.No. 5,573,922, issued to Hoess et al. on Nov. 12, 1996. Methods forattaching antibodies to surfaces are also art-known. See, Delamarche etal. Langmuir 12:1944-1946 (1996).

Targeting agents can be attached to the linkers of the invention by anyavailable reactive group. For example, peptides can be attached throughan amine, carboxyl, sulfhydryl, or hydroxyl group. Such a group canreside at a peptide terminus or at a site internal to the peptide chain.Nucleic acids can be attached through a reactive group on a base (e.g.,exocyclic amine) or an available hydroxyl group on a sugar moiety (e.g.,3′- or 5′-hydroxyl). The peptide and nucleic acid chains can be furtherderivatized at one or more sites to allow for the attachment ofappropriate reactive groups onto the chain. See, Chrisey et al. NucleicAcids Res. 24:3031-3039 (1996).

When the peptide or nucleic acid is a fully or partially syntheticmolecule, a reactive group or masked reactive group can be incorporatedduring the process of the synthesis. Many derivatized monomersappropriate for reactive group incorporation in both peptides andnucleic acids are know to those of skill in the art. See, for example,THE PEPTIDES: ANALYSIS, SYNTHESIS, BIOLOGY, Vol. 2: “Special Methods inPeptide Synthesis,” Gross, E. and Melenhofer, J., Eds., Academic Press,New York (1980). Many useful monomers are commercially available(Bachem, Sigma, etc.). This masked group can then be unmasked followingthe synthesis, at which time it becomes available for reaction with acomponent of a compound of the invention.

Exemplary nucleic acid targeting agents include aptamers, antisensecompounds, and nucleic acids that form triple helices. Typically, ahydroxyl group of a sugar residue, an amino group from a base residue,or a phosphate oxygen of the nucleotide is utilized as the neededchemical functionality to couple the nucleotide-based targeting agent tothe cytotoxin. However, one of skill in the art will readily appreciatethat other “non-natural” reactive functionalities can be appended to anucleic acid by conventional techniques. For example, the hydroxyl groupof the sugar residue can be converted to a mercapto or amino group usingtechniques well known in the art.

Aptamers (or nucleic acid antibody) are single- or double-stranded DNAor single-stranded RNA molecules that bind specific molecular targets.Generally, aptamers function by inhibiting the actions of the moleculartarget, e.g., proteins, by binding to the pool of the target circulatingin the blood. Aptamers possess chemical functionality and thus, cancovalently bond to cytotoxins, as described herein.

Although a wide variety of molecular targets are capable of formingnon-covalent but specific associations with aptamers, including smallmolecules drugs, metabolites, cofactors, toxins, saccharide-based drugs,nucleotide-based drugs, glycoproteins, and the like, generally themolecular target will comprise a protein or peptide, including serumproteins, kinins, eicosanoids, cell surface molecules, and the like.Examples of aptamers include Gilead's antithrombin inhibitor GS 522 andits derivatives (Gilead Science, Foster City, Calif.). See also, Macayaet al. Proc. Natl. Acad. Sci. USA 90:3745-9 (1993); Bock et al. Nature(London) 355:564-566 (1992) and Wang et al. Biochem. 32:1899-904 (1993).

Aptamers specific for a given biomolecule can be identified usingtechniques known in the art. See, e.g., Toole et al. (1992) PCTPublication No. WO 92/14843; Tuerk and Gold (1991) PCT Publication No.WO 91/19813; Weintraub and Hutchinson (1992) PCT Publication No.92/05285; and Ellington and Szostak, Nature 346:818 (1990). Briefly,these techniques typically involve the complexation of the moleculartarget with a random mixture of oligonucleotides. The aptamer-moleculartarget complex is separated from the uncomplexed oligonucleotides. Theaptamer is recovered from the separated complex and amplified. Thiscycle is repeated to identify those aptamer sequences with the highestaffinity for the molecular target.

For diseases that result from the inappropriate expression of genes,specific prevention or reduction of the expression of such genesrepresents an ideal therapy. In principle, production of a particulargene product may be inhibited, reduced or shut off by hybridization of asingle-stranded deoxynucleotide or ribodeoxynucleotide complementary toan accessible sequence in the mRNA, or a sequence within the transcriptthat is essential for pre-mRNA processing, or to a sequence within thegene itself. This paradigm for genetic control is often referred to asantisense or antigene inhibition. Additional efficacy is imparted by theconjugation to the nucleic acid of an alkylating agent, such as those ofthe present invention.

Antisense compounds are nucleic acids designed to bind and disable orprevent the production of the mRNA responsible for generating aparticular protein. Antisense compounds include antisense RNA or DNA,single or double stranded, oligonucleotides, or their analogs, which canhybridize specifically to individual mRNA species and preventtranscription and/or RNA processing of the mRNA species and/ortranslation of the encoded polypeptide and thereby effect a reduction inthe amount of the respective encoded polypeptide. Ching et al. Proc.Natl. Acad. Sci. U.S.A. 86:10006-10010 (1989); Broder et al. Ann. Int.Med. 113:604-618 (1990); Loreau et al. FEBS Letters 274:53-56 (1990);Holcenberg et al. WO91/11535; WO91/09865; WO91/04753; WO90/13641; WO91/13080, WO 91/06629, and EP 386563). Due to their exquisite targetsensitivity and selectivity, antisense oligonucleotides are useful fordelivering therapeutic agents, such as the cytotoxins of the inventionto a desired molecular target.

Others have reported that nucleic acids can bind to duplex DNA viatriple helix formation and inhibit transcription and/or DNA synthesis.Triple helix compounds (also referred to as triple strand drugs) areoligonucleotides that bind to sequences of double-stranded DNA and areintended to inhibit selectively the transcription of disease-causinggenes, such as viral genes, e.g., HIV and herpes simplex virus, andoncogenes, i.e., they stop protein production at the cell nucleus. Thesedrugs bind directly to the double stranded DNA in the cell's genome toform a triple helix and prevent the cell from making a target protein.See, e.g., PCT publications Nos. WO 92/10590, WO 92/09705, WO91/06626,and U.S. Pat. No. 5,176,996. Thus, the cytotoxins of the presentinvention are also conjugated to nucleic acid sequences that form triplehelices.

The site specificity of nucleic acids (e.g., antisense compounds andtriple helix drugs) is not significantly affected by modification of thephosphodiester linkage or by chemical modification of theoligonucleotide terminus. Consequently, these nucleic acids can bechemically modified; enhancing the overall binding stability, increasingthe stability with respect to chemical degradation, increasing the rateat which the oligonucleotides are transported into cells, and conferringchemical reactivity to the molecules. The general approach toconstructing various nucleic acids useful in antisense therapy has beenreviewed by van der Krol et al., Biotechniques 6:958-976 (1988) andStein et al. Cancer Res. 48:2659-2668 (1988). Therefore, in an exemplaryembodiment, the cytotoxins of the invention are conjugated to a nucleicacid by modification of the phosphodiester linkage.

Moreover, aptamers, antisense compounds and triple helix drugs bearingcytotoxins of the invention can also can include nucleotidesubstitutions, additions, deletions, or transpositions, so long asspecific hybridization to or association with the relevant targetsequence is retained as a functional property of the oligonucleotide.For example, some embodiments will employ phosphorothioate analogs whichare more resistant to degradation by nucleases than their naturallyoccurring phosphate diester counterparts and are thus expected to have ahigher persistence in vivo and greater potency (see, e.g., Campbell etal., J. Biochem. Biophys. Methods 20:259-267 (1990)). Phosphoramidatederivatives of oligonucleotides also are known to bind to complementarypolynucleotides and have the additional capability of accommodatingcovalently attached ligand species and will be amenable to the methodsof the present invention. See, for example, Froehler et al., NucleicAcids Res. 16(11):4831 (1988).

In some embodiments the aptamers, antisense compounds and triple helixdrugs will comprise O-methylribonucleotides (EP Publication No. 360609).Chimeric oligonucleotides may also be used (Dagle et al., Nucleic AcidsRes. 18: 4751 (1990)). For some applications, antisense oligonucleotidesand triple helix may comprise polyamide nucleic acids (Nielsen et al.,Science 254: 1497 (1991) and PCT publication No. WO 90/15065) or othercationic derivatives (Letsinger et al., J. Am. Chem. Soc. 110: 4470-4471(1988)). Other applications may utilize oligonucleotides wherein one ormore of the phosphodiester linkages has been substituted with anisosteric group, such as a 2-4 atom long internucleoside linkage asdescribed in PCT publication Nos. WO 92/05186 and 91/06556, or aformacetal group (Matteucci et al., J. Am. Chem. Soc. 113: 7767-7768(1991)) or an amide group (Nielsen et al., Science 254: 1497-1500(1991)).

In addition, nucleotide analogs, for example wherein the sugar or baseis chemically modified, can be employed in the present invention.“Analogous” forms of purines and pyrimidines are those generally knownin the art, many of which are used as chemotherapeutic agents. Anexemplary but not exhaustive list includes 4-acetylcytosine,5-(carboxyhydroxylmethyl) uracil, 5-fluorouracil, 5-bromouracil,5-carboxymethylaminomethyl-2-thiouracil,5-carboxymethylaminomethyluracil, dihydrouracil, inosine,N⁶-isopentenyladenine, 1-methyladenine, 1-methylpseudouracil,1-methylguanine, 1-methylinosine, 2,2-dimethylguanine, 2-methyladenine,2-methylguanine, 3-methylcytosine, 5-methylcytosine, N⁶-methyladenine,7-methylguanine, 5-methylaminomethyluracil,5-methoxyaminomethyl-2-thiouracil, β-D-mannosylqueosine, 5′methoxycarbonylmethyluracil, 5-methoxyuracil,2-methylthio-N⁶-isopentenyladenine, uracil-5-oxyacetic acid methylester,uracil-5-oxyacetic acid (v), wybutoxosine, pseudouracil, queosine,2-thiocytosine, 5-methyl-2-thiouracil, 2-thiouracil, 4-thiouracil,5-methyluracil, N-uracil-5-oxyacetic acid methylester,uracil-5-oxyacetic acid (v), pseudouracil, queosine, 2-thiocytosine, and2,6-diaminopurine. In addition, the conventional bases by halogenatedbases. Furthermore, the 2′-furanose position on the base can have anon-charged bulky group substitution. Examples of non-charged bulkygroups include branched alkyls, sugars and branched sugars.

Terminal modification also provides a useful procedure to conjugate thecytotoxins to the nucleic acid, modify cell type specificity,pharmacokinetics, nuclear permeability, and absolute cell uptake ratefor oligonucleotide pharmaceutical agents. For example, an array ofsubstitutions at the 5′ and 3′ ends to include reactive groups areknown, which allow covalent attachment of the cytotoxins. See, e.g.,OLIGODEOXYNUCLEOTIDES: ANTISENSE INHIBITORS OF GENE EXPRESSION, (1989)Cohen, Ed., CRC Press; PROSPECTS FOR ANTISENSE NUCLEIC ACID THERAPEUTICSFOR CANCER AND AIDS, (1991), Wickstrom, Ed., Wiley-Liss; GENEREGULATION: BIOLOGY OF ANTISENSE RNA AND DNA, (1992) Erickson and Izant,Eds., Raven Press; and ANTISENSE RNA AND DNA, (1992), Murray, Ed.,Wiley-Liss. For general methods relating to antisense compounds, see,ANTISENSE RNA AND DNA, (1988), D. A. Melton, Ed., Cold Spring HarborLaboratory, Cold Spring Harbor, N.Y.).

Detectable Labels

The particular label or detectable group used in conjunction with thecompounds and methods of the invention is generally not a criticalaspect of the invention, as long as it does not significantly interferewith the activity or utility of the compound of the invention. Thedetectable group can be any material having a detectable physical orchemical property. Such detectable labels have been well developed inthe field of immunoassays and, in general, most any label useful in suchmethods can be applied to the present invention. Thus, a label is anycomposition detectable by spectroscopic, photochemical, biochemical,immunochemical, electrical, optical or chemical means. Useful labels inthe present invention include magnetic beads (e.g., DYNABEADS™),fluorescent dyes (e.g., fluorescein isothiocyanate, Texas red,rhodamine, and the like), radiolabels (e.g., 3H, ¹²⁵I, ³⁵S, ¹⁴C, or³²P), enzymes (e.g., horse radish peroxidase, alkaline phosphatase andothers commonly used in an ELISA), and colorimetric labels such ascolloidal gold or colored glass or plastic beads (e.g., polystyrene,polypropylene, latex, etc.).

The label may be coupled directly or indirectly to a compound of theinvention according to methods well known in the art. As indicatedabove, a wide variety of labels may be used, with the choice of labeldepending on sensitivity required, ease of conjugation with thecompound, stability requirements, available instrumentation, anddisposal provisions.

When the compound of the invention is conjugated to a detectable label,the label is preferably a member selected from the group consisting ofradioactive isotopes, fluorescent agents, fluorescent agent precursors,chromophores, enzymes and combinations thereof. Methods for conjugatingvarious groups to antibodies are well known in the art. For example, adetectable label that is frequently conjugated to an antibody is anenzyme, such as horseradish peroxidase, alkaline phosphatase,β-galactosidase, and glucose oxidase.

Non-radioactive labels are often attached by indirect means. Generally,a ligand molecule (e.g., biotin) is covalently bound to a component ofthe conjugate. The ligand then binds to another molecules (e.g.,streptavidin) molecule, which is either inherently detectable orcovalently bound to a signal system, such as a detectable enzyme, afluorescent compound, or a chemiluminescent compound.

Components of the conjugates of the invention can also be conjugateddirectly to signal generating compounds, e.g., by conjugation with anenzyme or fluorophore. Enzymes of interest as labels will primarily behydrolases, particularly phosphatases, esterases and glycosidases, oroxidotases, particularly peroxidases. Fluorescent compounds includefluorescein and its derivatives, rhodamine and its derivatives, dansyl,umbelliferone, etc. Chemiluminescent compounds include luciferin, and2,3-dihydrophthalazinediones, e.g., luminol. For a review of variouslabeling or signal producing systems that may be used, see, U.S. Pat.No. 4,391,904.

Means of detecting labels are well known to those of skill in the art.Thus, for example, where the label is a radioactive label, means fordetection include a scintillation counter or photographic film as inautoradiography. Where the label is a fluorescent label, it may bedetected by exciting the fluorochrome with the appropriate wavelength oflight and detecting the resulting fluorescence. The fluorescence may bedetected visually, by means of photographic film, by the use ofelectronic detectors such as charge coupled devices (CCDs) orphotomultipliers and the like. Similarly, enzymatic labels may bedetected by providing the appropriate substrates for the enzyme anddetecting the resulting reaction product. Finally simple colorimetriclabels may be detected simply by observing the color associated with thelabel. Thus, in various dipstick assays, conjugated gold often appearspink, while various conjugated beads appear the color of the bead.

Fluorescent labels are presently preferred as they have the advantage ofrequiring few precautions in handling, and being amenable tohigh-throughput visualization techniques (optical analysis includingdigitization of the image for analysis in an integrated systemcomprising a computer). Preferred labels are typically characterized byone or more of the following: high sensitivity, high stability, lowbackground, low environmental sensitivity and high specificity inlabeling. Many fluorescent labels are commercially available from theSIGMA chemical company (Saint Louis, Mo.), Molecular Probes (Eugene,Oreg.), R&D systems (Minneapolis, Minn.), Pharmacia LKB Biotechnology(Piscataway, N.J.), CLONTECH Laboratories, Inc. (Palo Alto, Calif.),Chem Genes Corp., Aldrich Chemical Company (Milwaukee, Wis.), GlenResearch, Inc., GIBCO BRL Life Technologies, Inc. (Gaithersburg, Md.),Fluka Chemica-Biochemika Analytika (Fluka Chemie AG, Buchs,Switzerland), and Applied Biosystems (Foster City, Calif.), as well asmany other commercial sources known to one of skill. Furthermore, thoseof skill in the art will recognize how to select an appropriatefluorophore for a particular application and, if it not readilyavailable commercially, will be able to synthesize the necessaryfluorophore de novo or synthetically modify commercially availablefluorescent compounds to arrive at the desired fluorescent label.

In addition to small molecule fluorophores, naturally occurringfluorescent proteins and engineered analogues of such proteins areuseful in the present invention. Such proteins include, for example,green fluorescent proteins of cnidarians (Ward et al., Photochem.Photobiol. 35:803-808 (1982); Levine et al., Comp. Biochem. Physiol.,72B:77-85 (1982)), yellow fluorescent protein from Vibrio fischeristrain (Baldwin et al., Biochemistry 29:5509-15 (1990)),Peridinin-chlorophyll from the dinoflagellate Symbiodinium sp. (Morriset al., Plant Molecular Biology 24:673:77 (1994)), phycobiliproteinsfrom marine cyanobacteria, such as Synechococcus, e.g., phycoerythrinand phycocyanin (Wilbanks et al., J. Biol. Chem. 268:1226-35 (1993)),and the like.

Generally, prior to forming the linkage between the cytotoxin and thetargeting (or other) agent, and optionally, the spacer group, at leastone of the chemical functionalities will be activated. One skilled inthe art will appreciate that a variety of chemical functionalities,including hydroxy, amino, and carboxy groups, can be activated using avariety of standard methods and conditions. For example, a hydroxylgroup of the cytotoxin or targeting agent can be activated throughtreatment with phosgene to form the corresponding chloroformate, orp-nitrophenylchloroformate to form the corresponding carbonate.

In an exemplary embodiment, the invention makes use of a targeting agentthat includes a carboxyl functionality. Carboxyl groups may be activatedby, for example, conversion to the corresponding acyl halide or activeester. This reaction may be performed under a variety of conditions asillustrated in March, supra pp. 388-89. In an exemplary embodiment, theacyl halide is prepared through the reaction of the carboxyl-containinggroup with oxalyl chloride. The activated agent is reacted with acytotoxin or cytotoxin-linker arm combination to form a conjugate of theinvention. Those of skill in the art will appreciate that the use ofcarboxyl-containing targeting agents is merely illustrative, and thatagents having many other functional groups can be conjugated to thelinkers of the invention.

Reactive Functional Groups

For clarity of illustration the succeeding discussion focuses on theconjugation of a cytotoxin of the invention to a targeting agent. Thefocus exemplifies one embodiment of the invention from which, others arereadily inferred by one of skill in the art. No limitation of theinvention is implied, by focusing the discussion on a single embodiment.

Exemplary compounds of the invention bear a reactive functional group,which is generally located on a substituted or unsubstituted alkyl orheteroalkyl chain, allowing their facile attachment to another species.A convenient location for the reactive group is the terminal position ofthe chain.

Reactive groups and classes of reactions useful in practicing thepresent invention are generally those that are well known in the art ofbioconjugate chemistry. The reactive functional group may be protectedor unprotected, and the protected nature of the group may be changed bymethods known in the art of organic synthesis. Currently favored classesof reactions available with reactive cytotoxin analogues are those whichproceed under relatively mild conditions. These include, but are notlimited to nucleophilic substitutions (e.g., reactions of amines andalcohols with acyl halides, active esters), electrophilic substitutions(e.g., enamine reactions) and additions to carbon-carbon andcarbon-heteroatom multiple bonds (e.g., Michael reaction, Diels-Alderaddition). These and other useful reactions are discussed in, forexample, March, ADVANCED ORGANIC CHEMISTRY, 3rd Ed., John Wiley & Sons,New York, 1985; Hermanson, BIOCONJUGATE TECHNIQUES, Academic Press, SanDiego, 1996; and Feeney et al., MODIFICATION OF PROTEINS; Advances inChemistry Series, Vol. 198, American Chemical Society, Washington, D.C.,1982.

Exemplary reaction types include the reaction of carboxyl groups andvarious derivatives thereof including, but not limited to,N-hydroxysuccinimide esters, N-hydroxybenztriazole esters, acid halides,acyl imidazoles, thioesters, p-nitrophenyl esters, alkyl, alkenyl,alkynyl and aromatic esters. Hydroxyl groups can be converted to esters,ethers, aldehydes, etc. Haloalkyl groups are converted to new species byreaction with, for example, an amine, a carboxylate anion, thiol anion,carbanion, or an alkoxide ion. Dienophile (e.g., maleimide) groupsparticipate in Diels-Alder. Aldehyde or ketone groups can be convertedto imines, hydrazones, semicarbazones or oximes, or via such mechanismsas Grignard addition or alkyllithium addition. Sulfonyl halides reactreadily with amines, for example, to form sulfonamides. Amine orsulfhydryl groups are, for example, acylated, alkylated or oxidized.Alkenes, can be converted to an array of new species usingcycloadditions, acylation, Michael addition, etc. Epoxides react readilywith amines and hydroxyl compounds.

One skilled in the art will readily appreciate that many of theselinkages may be produced in a variety of ways and using a variety ofconditions. For the preparation of esters, see, e.g., March supra at1157; for thioesters, see, March, supra at 362-363, 491, 720-722, 829,941, and 1172; for carbonates, see, March, supra at 346-347; forcarbamates, see, March, supra at 1156-57; for amides, see, March supraat 1152; for ureas and thioureas, see, March supra at 1174; for acetalsand ketals, see, Greene et al. supra 178-210 and March supra at 1146;for acyloxyalkyl derivatives, see, PRODRUGS: TOPICAL AND OCULAR DRUGDELIVERY, K. B. Sloan, ed., Marcel Dekker, Inc., New York, 1992; forenol esters, see, March supra at 1160; for N-sulfonylimidates, see,Bundgaard et al., J. Med. Chem., 31:2066 (1988); for anhydrides, see,March supra at 355-56, 636-37, 990-91, and 1154; for N-acylamides, see,March supra at 379; for N-Mannich bases, see, March supra at 800-O₂, and828; for hydroxymethyl ketone esters, see, Petracek et al. Annals NYAcad. Sci., 507:353-54 (1987); for disulfides, see, March supra at 1160;and for phosphonate esters and phosphonamidates.

The reactive functional groups can be unprotected and chosen such thatthey do not participate in, or interfere with, the reactions.Alternatively, a reactive functional group can be protected fromparticipating in the reaction by the presence of a protecting group.Those of skill in the art will understand how to protect a particularfunctional group from interfering with a chosen set of reactionconditions. For examples of useful protecting groups, See Greene et al.,PROTECTIVE GROUPS IN ORGANIC SYNTHESIS, John Wiley & Sons, New York,1991.

Typically, the targeting agent is linked covalently to a cytotoxin usingstandard chemical techniques through their respective chemicalfunctionalities. Optionally, the linker or agent is coupled to the agentthrough one or more spacer groups. The spacer groups can be equivalentor different when used in combination.

Generally, prior to forming the linkage between the cytotoxin and thereactive functional group, and optionally, the spacer group, at leastone of the chemical functionalities will be activated. One skilled inthe art will appreciate that a variety of chemical functionalities,including hydroxy, amino, and carboxy groups, can be activated using avariety of standard methods and conditions. In an exemplary embodiment,the invention comprises a carboxyl functionality as a reactivefunctional group. Carboxyl groups may be activated as describedhereinabove.

Pharmaceutical Formulations and Administration

In another preferred embodiment, the present invention provides apharmaceutical formulation comprising a compound of the invention and apharmaceutically acceptable carrier.

The compounds described herein including pharmaceutically acceptablecarriers such as addition salts or hydrates thereof, can be delivered toa patient using a wide variety of routes or modes of administration.Suitable routes of administration include, but are not limited to,inhalation, transdermal, oral, rectal, transmucosal, intestinal andparenteral administration, including intramuscular, subcutaneous andintravenous injections. Preferably, the conjugates of the inventioncomprising an antibody or antibody fragment as the targeting moiety areadministered parenterally, more preferably intravenously.

As used herein, the terms “administering” or “administration” areintended to encompass all means for directly and indirectly delivering acompound to its intended site of action.

The compounds described herein, or pharmaceutically acceptable saltsand/or hydrates thereof, may be administered singly, in combination withother compounds of the invention, and/or in cocktails combined withother therapeutic agents. Of course, the choice of therapeutic agentsthat can be co-administered with the compounds of the invention willdepend, in part, on the condition being treated.

For example, when administered to patients suffering from a diseasestate caused by an organism that relies on an autoinducer, the compoundsof the invention can be administered in cocktails containing agents usedto treat the pain, infection and other symptoms and side effectscommonly associated with the disease. Such agents include, e.g.,analgesics, antibiotics, etc.

When administered to a patient undergoing cancer treatment, thecompounds may be administered in cocktails containing anti-cancer agentsand/or supplementary potentiating agents. The compounds may also beadministered in cocktails containing agents that treat the side-effectsof radiation therapy, such as anti-emetics, radiation protectants, etc.

Supplementary potentiating agents that can be co-administered with thecompounds of the invention include, e.g., tricyclic anti-depressantdrugs (e.g., imipramine, desipramine, amitriptyline, clomipramine,trimipramine, doxepin, nortriptyline, protriptyline, amoxapine andmaprotiline); non-tricyclic and anti-depressant drugs (e.g., sertraline,trazodone and citalopram); Ca⁺² antagonists (e.g., verapamil,nifedipine, nitrendipine and caroverine); amphotericin; triparanolanalogues (e.g., tamoxifen); antiarrhythmic drugs (e.g., quinidine);antihypertensive drugs (e.g., reserpine); thiol depleters (e.g.,buthionine and sulfoximine); and calcium leucovorin.

The active compound(s) of the invention are administered per se or inthe form of a pharmaceutical composition wherein the active compound(s)is in admixture with one or more pharmaceutically acceptable carriers,excipients or diluents. Pharmaceutical compositions for use inaccordance with the present invention are typically formulated in aconventional manner using one or more physiologically acceptablecarriers comprising excipients and auxiliaries, which facilitateprocessing of the active compounds into preparations which, can be usedpharmaceutically. Proper formulation is dependent upon the route ofadministration chosen.

For transmucosal administration, penetrants appropriate to the barrierto be permeated are used in the formulation. Such penetrants aregenerally known in the art.

For oral administration, the compounds can be formulated readily bycombining the active compound(s) with pharmaceutically acceptablecarriers well known in the art. Such carriers enable the compounds ofthe invention to be formulated as tablets, pills, dragees, capsules,liquids, gels, syrups, slurries, suspensions and the like, for oralingestion by a patient to be treated. Pharmaceutical preparations fororal use can be obtained solid excipient, optionally grinding aresulting mixture, and processing the mixture of granules, after addingsuitable auxiliaries, if desired. to obtain tablets or dragee cores.Suitable excipients are, in particular, fillers such as sugars,including lactose, sucrose, mannitol, or sorbitol; cellulosepreparations such as, for example, maize starch, wheat starch, ricestarch, potato starch, gelatin, gum tragacanth, methyl cellulose,hydroxypropylmethyl-cellulose, sodium carboxymethylcellulose, and/orpolyvinylpyrrolidone (PVP). If desired, disintegrating agents may beadded, such as the cross-linked polyvinyl pyrrolidone, agar, or alginicacid or a salt thereof such as sodium alginate.

Dragee cores are provided with suitable coatings. For this purpose,concentrated sugar solutions may be used, which may optionally containgum arabic, talc, polyvinyl pyrrolidone, carbopol gel, polyethyleneglycol, and/or titanium dioxide, lacquer solutions, and suitable organicsolvents or solvent mixtures. Dyestuffs or pigments may be added to thetablets or dragee coatings for identification or to characterizedifferent combinations of active compound doses.

Pharmaceutical preparations, which can be used orally, include push-fitcapsules made of gelatin, as well as soft, sealed capsules made ofgelatin and a plasticizer, such as glycerol or sorbitol. The push-fitcapsules can contain the active ingredients in admixture with fillersuch as lactose, binders such as starches, and/or lubricants such astalc or magnesium stearate and, optionally, stabilizers. In softcapsules, the active compounds may be dissolved or suspended in suitableliquids, such as fatty oils, liquid paraffin, or liquid polyethyleneglycols. In addition, stabilizers may be added. All formulations fororal administration should be in dosages suitable for suchadministration.

For buccal administration, the compositions may take the form of tabletsor lozenges formulated in conventional manner.

For administration by inhalation, the compounds for use according to thepresent invention are conveniently delivered in the form of an aerosolspray presentation from pressurized packs or a nebulizer, with the useof a suitable propellant, e.g., dichlorodifluoromethane,trichlorofluoromethane, dichlorotetrafluoroethane, carbon dioxide orother suitable gas. In the case of a pressurized aerosol the dosage unitmay be determined by providing a valve to deliver a metered amount.Capsules and cartridges of e.g., gelatin for use in an inhaler orinsufflator may be formulated containing a powder mix of the compoundand a suitable powder base such as lactose or starch.

The compounds may be formulated for parenteral administration byinjection, e.g., by bolus injection or continuous infusion. Injection isa preferred method of administration for the compositions of the currentinvention. Formulations for injection may be presented in unit dosageform, e.g., in ampoules or in multi-dose containers, with an addedpreservative. The compositions may take such forms as suspensions,solutions or emulsions in oily or aqueous vehicles, and may containformulatory agents such as suspending, stabilizing and/or dispersingagents may be added, such as the cross-linked polyvinyl pyrrolidone,agar, or alginic acid or a salt thereof such as sodium alginate.

Pharmaceutical formulations for parenteral administration includeaqueous solutions of the active compounds in water-soluble form.Additionally, suspensions of the active compounds may be prepared asappropriate oily injection suspensions. Suitable lipophilic solvents orvehicles include fatty oils such as sesame oil, or synthetic fatty acidesters, such as ethyl oleate or triglycerides, or liposomes. Aqueousinjection suspensions may contain substances, which increase theviscosity of the suspension, such as sodium carboxymethyl cellulose,sorbitol, or dextran. Optionally, the suspension may also containsuitable stabilizers or agents, which increase the solubility of thecompounds to allow for the preparation of highly, concentratedsolutions. For injection, the agents of the invention may be formulatedin aqueous solutions, preferably in physiologically compatible bufferssuch as Hanks's solution, Ringer's solution, or physiological salinebuffer.

Alternatively, the active ingredient may be in powder form forconstitution with a suitable vehicle, e.g., sterile pyrogen-free water,before use.

The compounds may also be formulated in rectal compositions such assuppositories or retention enemas, e.g., containing conventionalsuppository bases such as cocoa butter or other glycerides.

In addition to the formulations described previously, the compounds mayalso be formulated as a depot preparation. Such long acting formulationsmay be administered by implantation or transcutaneous delivery (e.g.,subcutaneously or intramuscularly), intramuscular injection or atransdermal patch. Thus, for example, the compounds may be formulatedwith suitable polymeric or hydrophobic materials (e.g., as an emulsionin an acceptable oil) or ion exchange resins, or as sparingly solublederivatives, for example, as a sparingly soluble salt.

The pharmaceutical compositions also may comprise suitable solid or gelphase carriers or excipients. Examples of such carriers or excipientsinclude but are not limited to calcium carbonate, calcium phosphate,various sugars, starches, cellulose derivatives, gelatin, and polymerssuch as polyethylene glycols.

A preferred pharmaceutical composition is a composition formulated forinjection such as intravenous injection and includes about 0.01% toabout 100% by weight of the drug-ligand conjugate, based upon 100%weight of total pharmaceutical composition. The drug-ligand conjugatemay be an antibody-cytotoxin conjugate where the antibody has beenselected to target a particular cancer.

Libraries

Also within the scope of the present invention are libraries of thecytotoxin, cytotoxin-linker and agent-linker conjugates of thecytotoxins and linkers of the invention. Exemplary libraries include atleast 10 compounds, more preferably at least 100 compound, even morepreferably at least 1000 compounds and still more preferably at least100,000 compounds. The libraries in a form that is readily queried for aparticular property, e.g., cytotoxicity, cleavage of a linker by anenzyme, or other cleavage reagent. Exemplary forms include chip formats,microarrays, and the like.

Parallel, or combinatorial, synthesis has as its primary objective thegeneration of a library of diverse molecules which all share a commonfeature, referred to throughout this description as a scaffold. Bysubstituting different moieties at each of the variable parts of thescaffold molecule, the amount of space explorable in a library grows.Theories and modern medicinal chemistry advocate the concept of occupiedspace as a key factor in determining the efficacy of a given compoundagainst a given biological target. By creating a diverse library ofmolecules, which explores a large percentage of the targeted space, theodds of developing a highly efficacious lead compound increasedramatically.

Parallel synthesis is generally conducted on a solid phase support, suchas a polymeric resin. The scaffold, or other suitable intermediate iscleavably tethered to the resin by a chemical linker. Reactions arecarried out to modify the scaffold while tethered to the particle.Variations in reagents and/or reaction conditions produce the structuraldiversity, which is the hallmark of each library.

Parallel synthesis of “small” molecules (non-oligomers with a molecularweight of 200-1000) was rarely attempted prior to 1990. See, forexample, Camps. et al., Annaks de Quimica, 70: 848 (1990). Recently,Ellmann disclosed the solid phase-supported parallel (also referred toas “combinatorial”) synthesis of eleven benzodiazepine analogs alongwith some prostaglandins and beta-turn mimetics. These disclosures areexemplified in U.S. Pat. No. 5,288,514. Another relevant disclosure ofparallel synthesis of small molecules may be found in U.S. Pat. No.5,324,483. This patent discloses the parallel synthesis of between 4 and40 compounds in each of sixteen different scaffolds. Chen et al. havealso applied organic synthetic strategies to develop non-peptidelibraries synthesized using multi-step processes on a polymer support.(Chen et al., J. Am. Chem. Soc., 116: 2661-2662 (1994)).

Once a library of unique compounds is prepared, the preparation of alibrary of immunoconjugates, or antibodies can be prepared using thelibrary of autoinducers as a starting point and using the methodsdescribed herein.

Kits

In another aspect, the present invention provides kits containing one ormore of the compounds or compositions of the invention and directionsfor using the compound or composition. In an exemplary embodiment, theinvention provides a kit for conjugating a linker arm of the inventionto another molecule. The kit includes the linker, and directions forattaching the linker to a particular functional group. The kit may alsoinclude one or more of a cytotoxic drug, a targeting agent, a detectablelabel, pharmaceutical salts or buffers. The kit may also include acontainer and optionally one or more vial, test tube, flask, bottle, orsyringe. Other formats for kits will be apparent to those of skill inthe art and are within the scope of the present invention.

Purification

In another exemplary embodiment, the present invention provides a methodfor isolating a molecular target for a ligand-cytotoxin of theinvention, which binds to the ligand X⁴. The method preferablycomprises, contacting a cellular preparation that includes the targetwith an immobilized compound, thereby forming a complex between thereceptor and the immobilized compound.

The cytotoxin of the invention can be immobilized on an affinity supportby any art-recognized means. Alternatively, the cytotoxin can beimmobilized using one or more of the linkers of the invention.

In yet another exemplary embodiment, the invention provides an affinitypurification matrix that includes a linker of the invention.

The method of the invention for isolating a target will typicallyutilize one or more affinity chromatography techniques. Affinitychromatography enables the efficient isolation of species such asbiological molecules or biopolymers by utilizing their recognition sitesfor certain supported chemical structures with a high degree ofselectivity. The literature is replete with articles, monographs, andbooks on the subject of affinity chromatography, including such topicsas affinity chromatography supports, crosslinking members, ligands andtheir preparation and use. A sampling of those references includes:Ostrove, Methods Enzymol. 182: 357-71 (1990); Ferment, Bioeng. 70:199-209 (1990). Huang et al., J. Chromatogr. 492: 431-69 (1989);“Purification of enzymes by heparin-Sepharose affinity chromatography,”J. Chromatogr., 184: 335-45 (1980); Farooqi, Enzyme Eng., 4: 441-2(1978); Nishikawa, Chem. Technol., 5(9): 564-71 (1975); Guilford et al.,in, PRACT. HIGH PERFORM. LIQ. CHROMATOGR., Simpson (ed.), 193-206(1976); Nishikawa, Proc. Int. Workshop Technol. Protein Sep. Improv.Blood Plasma Fractionation, Sandberg (ed.), 422-35; (1977) “Affinitychromatography of enzymes,” Affinity Chromatogr., Proc. Int. Symp.25-38, (1977) (Pub. 1978); and AFFINITY CHROMATOGRAPHY: A PRACTICALAPPROACH, Dean et al. (ed.), IRL Press Limited, Oxford, England (1985).Those of skill in the art have ample guidance in developing particularaffinity chromatographic methods utilizing the materials of theinvention.

In the present method, affinity chromatographic media of varyingchemical structures can be used as supports. For example, agarose gelsand cross-linked agarose gels are useful as support materials, becausetheir hydrophilicity makes them relatively free of nonspecific binding.Other useful supports include, for example, controlled-pore glass (CPG)beads, cellulose particles, polyacrylamide gel beads and Sephadex™ gelbeads made from dextran and epichlorohydrin.

Drug-Ligand Conjugate Methods of Use

In addition to the compositions and constructs described above, thepresent invention also provides a number of methods that can bepracticed utilizing the compounds and conjugates of the invention.Methods for using the drug-ligand conjugate of the current inventioninclude: killing or inhibiting the growth or replication of a tumor cellor cancer cell, treating cancer, treating a pre-cancerous condition,killing or inhibiting the growth or replication of a cell that expressesan auto-immune antibody, treating an autoimmune disease, treating aninfectious disease, preventing the multiplication of a tumor cell orcancer cell, preventing cancer, preventing the multiplication of a cellthat expresses an auto-immune antibody, preventing an autoimmunedisease, and preventing an infectious disease. These methods of usecomprise administering to an animal such as a mammal or a human in needthereof an effective amount of a drug-ligand conjugate. Preferredligands for many of the methods of use described herein includeantibodies and antibody fragments which target the particular tumorcell, cancer cell, or other target area.

The drug-ligand complex of the current invention is useful for treatingcancer, autoimmune disease and infectious disease in an animal.Compositions and methods for treating tumors by providing a subject thecomposition in a pharmaceutically acceptable manner, with apharmaceutically effective amount of a composition of the presentinvention are provided.

The current invention is particularly useful for the treatment of cancerand for the inhibition of the multiplication of a tumor cell or cancercell in an animal. Cancer, or a precancerous condition, includes, but isnot limited to, a tumor, metastasis, or any disease or disordercharacterized by uncontrolled cell growth, can be treated or preventedby administration the drug-ligand complex of the current invention. Thecomplex delivers the drug a tumor cell or cancer cell. In oneembodiment, the ligand specifically binds to or associates with acancer-cell or a tumor-cell-associated antigen. Because of its closeproximity to the ligand, the drug can be taken up inside a tumor cell orcancer cell through, for example, receptor-mediated endocytosis. Theantigen can be attached to a tumor cell or cancer cell or can be anextracellular matrix protein associated with the tumor cell or cancercell. Once inside the cell, the linker is hydrolytically cleaved by atumor-cell or cancer-cell-associated proteases, thereby releasing thedrug. The released drug is then free to diffuse and induce cytotoxicactivities. In an alternative embodiment, the drug is cleaved from thedrug-ligand complex outside the tumor cell or cancer cell, and the drugsubsequently penetrates the cell.

The ligand may bind to, for example, a tumor cell or cancer cell, atumor cell or cancer cell antigen which is on the surface of the tumorcell or cancer cell, or a tumor cell or cancer cell antigen which is anextracellular matrix protein associated with the tumor cell or cancercell. The ligand can be designed specifically for a particular tumorcell or cancer cell type. Therefore, the type of tumors or cancers thatcan be effectively treated can be altered by the choice of ligand.

Representative examples of precancerous conditions that may be targetedby the drug-ligand conjugate, include, but are not limited to:metaplasia, hyperplasia, dysplasia, colorectal polyps, actinicketatosis, actinic cheilitis, human papillomaviruses, leukoplakia,lychen planus and Bowen's disease.

Representative examples of cancers or tumors that may be targeted by thedrug-ligand conjugate include, but are not limited to: lung cancer,colon cancer, prostate cancer, lymphoma, melanoma, breast cancer,ovarian cancer, testicular cancer, CNS cancer, renal cancer, kidneycancer, pancreatic cancer, stomach cancer, oral cancer, nasal cancer,cervical cancer and leukemias. It will be readily apparent to theordinarily skilled artisan that the particular targeting ligand used inthe conjugate can be chosen such that it targets the drug to the tumortissue to be treated with the drug (i.e., a targeting agent specific fora tumor-specific antigen is chosen). Examples of such targeting ligandsare well known in the art, non-limiting examples of which includeanti-Her2 for treatment of breast cancer, anti-CD20 for treatment oflymphoma, anti-PSMA for treatment of prostate cancer and anti-CD30 fortreatment of lymphomas, including non-Hodgkin's lymphoma.

In an embodiment, the present invention provides a method of killing acell. The method includes administering to the cell an amount of acompound of the invention sufficient to kill said cell. In an exemplaryembodiment, the compound is administered to a subject bearing the cell.In a further exemplary embodiment, the administration serves to retardor stop the growth of a tumor that includes the cell (e.g., the cell canbe a tumor cell). For the administration to retard the growth, the rateof growth of the cell should be at least 10% less than the rate ofgrowth before administration. Preferably, the rate of growth will beretarded at least 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or completelystopped.

Effective Dosages

Pharmaceutical compositions suitable for use with the present inventioninclude compositions wherein the active ingredient is contained in atherapeutically effective amount, i.e., in an amount effective toachieve its intended purpose. The actual amount effective for aparticular application will depend, inter alfa, on the condition beingtreated. Determination of an effective amount is well within thecapabilities of those skilled in the art, especially in light of thedetailed disclosure herein.

For any compound described herein, the therapeutically effective amountcan be initially determined from cell culture assays. Target plasmaconcentrations will be those concentrations of active compound(s) thatare capable of inhibition cell growth or division. In preferredembodiments, the cellular activity is at least 25% inhibited. Targetplasma concentrations of active compound(s) that are capable of inducingat least about 50%, 75%, or even 90% or higher inhibition of cellularactivity are presently preferred. The percentage of inhibition ofcellular activity in the patient can be monitored to assess theappropriateness of the plasma drug concentration achieved, and thedosage can be adjusted upwards or downwards to achieve the desiredpercentage of inhibition.

As is well known in the art, therapeutically effective amounts for usein humans can also be determined from animal models. For example, a dosefor humans can be formulated to achieve a circulating concentration thathas been found to be effective in animals. The dosage in humans can beadjusted by monitoring cellular inhibition and adjusting the dosageupwards or downwards, as described above.

A therapeutically effective dose can also be determined from human datafor compounds which are known to exhibit similar pharmacologicalactivities. The applied dose can be adjusted based on the relativebioavailability and potency of the administered compound as comparedwith the known compound.

Adjusting the dose to achieve maximal efficacy in humans based on themethods described above and other methods as are well-known in the artis well within the capabilities of the ordinarily skilled artisan.

In the case of local administration, the systemic circulatingconcentration of administered compound will not be of particularimportance. In such instances, the compound is administered so as toachieve a concentration at the local area effective to achieve theintended result.

For use in the prophylaxis and/or treatment of diseases related toabnormal cellular proliferation, a circulating concentration ofadministered compound of about 0.001 μM to 20 μM is preferred, withabout 0.01 μM to 5 μM being preferred.

Patient doses for oral administration of the compounds described herein,typically range from about 1 mg/day to about 10,000 mg/day, moretypically from about 10 mg/day to about 1,000 mg/day, and most typicallyfrom about 50 mg/day to about 500 mg/day. Stated in terms of patientbody weight, typical dosages range from about 0.01 to about 150mg/kg/day, more typically from about 0.1 to about 15 mg/kg/day, and mosttypically from about 1 to about 10 mg/kg/day for example 5 mg/kg/day or3 mg/kg/day

For other modes of administration, dosage amount and interval can beadjusted individually to provide plasma levels of the administeredcompound effective for the particular clinical indication being treated.For example, in one embodiment, a compound according to the inventioncan be administered in relatively high concentrations multiple times perday. Alternatively, it may be more desirable to administer a compound ofthe invention at minimal effective concentrations and to use a lessfrequent administration regimen. This will provide a therapeutic regimenthat is commensurate with the severity of the individual's disease.

Utilizing the teachings provided herein, an effective therapeutictreatment regimen can be planned which does not cause substantialtoxicity and yet is entirely effective to treat the clinical symptomsdemonstrated by the particular patient. This planning should involve thecareful choice of active compound by considering factors such ascompound potency, relative bioavailability, patient body weight,presence and severity of adverse side effects, preferred mode ofadministration and the toxicity profile of the selected agent.

The compounds, compositions and methods of the present invention arefurther illustrated by the examples that follow. These examples areoffered to illustrate, but not to limit the claimed invention.

EXAMPLES Material and Methods

In the examples below, unless otherwise stated, temperatures are givenin degrees Celsius (° C.); operations were carried out at room orambient temperature (typically a range of from about 18-25° C.;evaporation of solvent was carried out using a rotary evaporator underreduced pressure (typically, 4.5-30 mmHg) with a bath temperature of upto 60° C.; the course of reactions was typically followed by TLC andreaction times are provided for illustration only; melting points areuncorrected; products exhibited satisfactory ¹H-NMR and/ormicroanalytical data; yields are provided for illustration only; and thefollowing conventional abbreviations are also used: mp (melting point),L (liter(s)), mL (milliliters), mmol (millimoles), g (grams), mg(milligrams), min (minutes), LC-MS (liquid chromatography-massspectrometry) and h (hours).

¹H-NMR spectra were measured on a Varian Mercury 300 MHz spectrometerand were consistent with the assigned structures. Chemical shifts werereported in parts per million (ppm) downfield from tetramethylsilane.Electrospray mass spectra were recorded on a Perkin Elmer Sciex API 365mass spectrometer. Elemental analyses were performed by RobertsonMicrolit Laboratories, Madison, N.J. Silica gel for flash chromatographywas E. Merck grade (230-400 mesh). Reverse-Phase analytical HPLC wasperformed on either a HP 1100 or a Varian ProStar 210 instrument with aPhenomenex Luna 5 μm C-18(2) 150 mm×4.6 mm column or a VarianMicrosorb-MV 0.1 μm C-18 150 mm×4.6 mm column. A flow rate of 1 mL/minwas with either a gradient of 0% to 50% buffer B over 15 minutes or 10%to 100% buffer B over 10 minutes with detection by UV at 254 nm. BufferA, 20 mM ammonium formate+20% acetonitrile or 0.1% trifluoroacetic acidin acetonitrile; buffer B, 20 mM ammonium formate+80% acetonitrile or0.1% aqueous trifluoroacetic acid. Reverse phase preparative HPLC wereperformed on a Varian ProStar 215 instrument with a Waters Delta Pak 15μm C-18 300 mm×7.8 mm column.

Example 1 Synthesis of Peptide Linker Conjugates

1.1a Synthesis Methodology

1.1b Synthesis of Compound 1:N-[2′-(N′-tert-butoxycarbonyl-animo)-ethyl]-valine tert-butyl ester.

To a solution of 2-(N-tert-butoxycarbonyl-amino)-ethyl bromide (1 g, 4.5mmole) and valine tert-butyl ester (0.936 g, 4.5 mmole) in DMF (10 mL)was added potassium carbonate (1.85 g, 13.5 mmole). The mixture thusobtained was stirred at 100° C. overnight. The reaction mixture wasconcentrated and the residue was purified by flash chromatography onsilica gel with ethyl acetate/hexanes (3/7) as eluent to give the titlecompound as an oil (0.16 g, 12%). ¹H NMR (CDCl₃) δ 0.94 (ft, 6H), 1.44(s, 9H), 1.473 and 1.475 (2s, 9H), 1.88 (m, 1H), 2.51 (m, 1H), 2.78 (m,2H), 3.11 (m, 1H), 3.22 (m, 1H), 3.39 and 4.13 (2bt, 1H), 5.00 (bs, 1H)ppm; LC-MS (ESI) 205 (M+H⁺-112), 261 (M+H⁺-Bu), 317 (M+H⁺).

1.1c Synthesis of Compound 2: N-(2-Aminoethyl)-valine.

The compound 1 (137 mg, 0.43 mmole) was dissolved in a solution ofTFA/dichloromethane (2 mL, 1/1) at room temperature. The mixture thusobtained was stirred at room temperature for 30 min. The reactionmixture was concentrated to dryness to give the title compound as an oil(0.18 g, 95%) ¹H NMR (CD₃OD) δ 1.07 and 1.16 (2d, 6H), 2.35 (m, 1H), 3.2(m, 1H), 3.38 (m, 4H) ppm; LC-MS (ESI) 217 (M+H⁺).

1.1d Synthesis of Compound 3.

To a solution of maleamide-dPEG₄-NHS ester (61 mg, 0.16 mmole) indichloromethane (2 mL) was added dropwise compound 2 (80.7 mg, 0.16mmole) and diisopropylethylamine (55.5 μL, 0.32 mmole) indichloromethane (1 mL). The mixture thus obtained was stirred overnight.The solvent were removed on the rotovap, and the residue was purified byflash chromatography on silica gel with dichloromethane, followed by 5%methanol in dichloromethane and finally 100% methanol as eluent to givethe title compound as colorless oil (87 mg, 97%). ¹H NMR (CDCl₃) δ 1.08(dd, 6H), 2.25 (m, 1H), 2.49 (t, 2H), 2.52 (t, 2H), 3.10-3.79 (m, 25H),6.82 (s, 2H) ppm; LC-MS (ESI) 559 (M+H⁺)

1.1e Synthesis of Compound 4: Fmoc-Cit-PABOH.

To a solution of Fmoc-Cit-OH (1.0 g, 2.52 mmole) and4-aminobenzylalcohol (341 mg, 2.77 mmole) in dichloromethane (10 mL) andmethanol (5 mL) was added2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline[EEDQ] (1.24 g, 5.04mmole) in one portion. The mixture was stirred in the dark for 16 hours.The solvents were removed on the rotovap, and the white solid wastriturated with ether (100 mL). The resulting suspension was sonicatedfor 5 min and then left to stand for 30 min. The white solid wascollected by filtration, washed with ether and dried in vacuo (1.23 g,97%). ¹H-NMR (DMSO) δ 1.32 to 1.52 (m, 2H), 1.52 to 1.74 (dm, 2H), 2.86to 3.06 (dm, 2H), 4.1 (M, 1H), 4.42 (d, 2H), 5.07 (t, 1H), 5.40 (bs,2H), 5.97 (t, 1H), 7.19 to 7.95 (m, 12H), 8.10 (d, 1H), 9.97 (s, 1H)ppm; LC-MS (ESI) 503.1 (M+H⁺).

1.1f Synthesis of Compound 5: Fmoc-Cit-PABC-PNP.

To a solution of Compound 4 (309 mg, 0.62 mmole) andp-nitrophenylchloroformate (372 mg, 1.85 mmole) in Tetrahydrofuran (30mL) and 1-methyl-2-pyrrolidine (1 mL) was added pyridine (100 μL, 1.23mmole) in one portion. The mixture thus obtained was stirred at roomtemperature for 30 minutes. The solvents were removed on the rotovap,and the residue was purified by flash chromatography on silica gel withdichloromethane, followed by 3% methanol in dichloromethane and finally10% methanol in dichloromethane as eluent to give the title compound asa white solid (97.9 mg, 70%). LC-MS (ESI) 668 (M+H⁺).

1.1g Synthesis of Compound 6: Fmoc-Lys(Boc)-PABOH.

Compound 6 was prepared as described above for Compound 4 in 98% yield.¹H NMR (DMSO) δ 1.40 (s, 9H), 1.38 (m, 2H), 1.50 to 1.74 (dm, 2H), 3.04(t, 2H), 3.30 (q, 3H), 4.19 to 4.31 (m, 2H), 4.41 (d, 2H), 4.55 (s, 2H),7.28 to 7.68 (m, 12H), 8.00 (d, 1H) ppm; LC-MS (ESI) 574 (M+H⁺).

1.1h Synthesis of Compound 7: Fmoc-Lys(Boc)-PABC-PNP.

Compound 7 was prepared as described above for Compound 5 in 70% yield.¹H NMR (CD₃Cl) δ 1.44 (s, 9H), 1.49-1.60 (m, 6H), 1.73 (m, 1H), 2.00 (m,1H), 3.11 (m, 1H), 3.20 (bs, 1H), 4.23 (m, 2H), 4.46 (bs, 2H), 4.67 (bs,1H), 5.56 (bs, 1H), 7.28 (m, 2H), 7.36-7.41 (m, 6H), 7.59 (m, 4H), 7.76(d, 2H), 8.26 (dd, 2H), 8.45 (bs, 1H) ppm; LC-MS (ESI) 639 (M+H⁺-Boc),684 (M+H⁺-Bu), 739 (M+H⁺), 778 (M+K⁺).

1.1i Synthesis of Compound 8: Boc-Val-Cit-OH.

To a solution of Citrulline (2.54 g, 14.50 mmole) and Sodium Bicarbonate(1.28 g) in water (40 mL) was added Boc-Val-OSu (4.34 g, 13.81 mmole)dissolved in dimethoxyethane (DME). To aid the solubility of the mixturetetrahydrofuran (10 mL) was added. The mixture thus obtained was letstir overnight at room temperature. Aqueous citric acid (15%, 75 mL) wasadded and the mixture was extracted with 10% 2-propanol/ethyl acetate(2×100 mL). The organic layer was washed with brine (2×150 mL) and thesolvents were removed on the rotovap. The resulting white solid wasdried in vacuo for 5 hours and then treated with ether (100 mL). Afterbrief sonication and trituration, the white solid product was collectedby filtration (1.39 g, 27%). ¹H NMR (CD₃OD) δ 0.91 (dd, 3H), 0.98 (dd,3H), 1.44 (s, 9H), 1.70 (m, 2H), 1.87 (m, 2H), 2.02 (m, 2H), 3.11 (t,2H), 3.89 (t, 1H), 4.39 (q, 1H), 8.22 (d, 1H) ppm; LC-MS (ESI) 375(M+H⁺).

1.1j Synthesis of Compound 9: Boc-Val-Cit-PABOH.

Compound 9 was prepared as described above for Compound 4 in 71% yield.¹H NMR (CD₃OD) δ 0.93 and 0.97 (2d, 6H), 1.44 (s, 9H), 1.58 (m, 2H),1.75 (m, 1H), 1.90 (m, 1H), 2.05 (m, 1H), 3.10 (m, 1H), 3.19 (m, 1H),3.91 (d, 1H), 4.52 (m, 1H), 5.25 (s, 2H), 7.40 (d, 2H), 7.45 (dd, 2H),7.64 (d, 4H), 8.29 (dd, 2H) ppm; LC-MS (ESI) 480 (M+H⁺).

1.1k Synthesis of Compound 10: Boc-Val-Cit-PABC-PNP.

A solution of Boc-Val-Cit-PABOH (178 mg, 0.370 mmole) in THF (8 mL) inCH₂Cl₂ (4 mL) was stirred at room temperature with PNP chloroformate(160 mg, 0.80 mmole) and pyridine (65 μL, 0.80 mmole) for 3 h. Ethylacetate (100 mL) and 10% aqueous citric acid (50 mL) were added to thereaction mixture and organic layer was washed with brine, dried andconcentrated and the residue was purified by flash chromatography onsilica gel with 5% methanol in as eluent to give the title compound as awhite solid (165 mg, 70%). ¹H NMR (CD₃OD) δ 0.93 (dd, 3H), 0.97 (dd,3H), 1.44 (s, 9H), 1.58 (m, 2H), 1.75 (m, 1H), 1.89 (m, 1H), 2.05 (m,1H), 3.10 (m, 1H), 3.20 (m, 1H), 3.90 (d, 1H), 4.51 (m, 1H), 4.55 (s,2H), 7.29 (d, 2H), 7.55 (d, 2H) ppm; LC-MS (ESI) 545 (M+H⁺-Boc), 645(M+H⁺), 667 (M+Na⁺), 683 (M+K⁺).

1.1l Synthesis of Compound 12a.

To a suspension of Compound 11 (20 mg, 0.078 mmole) in ethyl acetate (5mL) was bubbled HCl gas for 20 min (by the time, the suspension becameto a clean solution). The reaction mixture was stirred for additional 5min then the mixture was concentrated to dryness to give the titlecompound as yellow solid (26 mg, 100%) which was used in next stepwithout further purification. LC-MS (ESI) 260 (M+H⁺—CO, 295 (M+H⁺).

1.1m Synthesis of Compound 12b.

To a suspension of Compound 11 (20 mg, 0.078 mmole) in ethyl acetate (5mL) was bubbled HBr gas for 20 min (by the time, the suspension becameto a clean solution). The reaction mixture was stirred for additional 5min then the mixture was concentrated to dryness to give the titlecompound as yellow solid (33 mg, 100%) which was used in next stepwithout further purification. LC-MS (ESI) 260 (M+H⁺-Br), 339 (M+H⁺), 341(M+H⁺+2).

1.1n Synthesis of Compound 13b.

To a solution of Compound 12a (26 mg, 0.078 mmole) in DMF (2 mL) wereadded 5-(2-dimethylamino-ethoxy)-benzofuran-2-carboxylic acid (44 mg,0.155 mmole) and EDC (30 mg, 0.155 mmole). The mixture thus obtained wasstirred at room temperature for 2 h. The mixture was concentrated andthe residue was dissolved in H₂O/CH₃CN/TFA (4/1.5/0.5, 6 mL) and it wasplaced in freezer for 3 h. A yellow solid was collected by filtration(35 mg, 85%). ¹H NMR (CD₃OD) δ 2.67 (s, 3H), 3.01 (s, 6H), 3.34 (m, 2H),3.63 (ft, 1H), 3.89 (s, 3H), 3.91 (m, 1H), 4.41 (m, 3H), 4.54 (m, 1H),4.65 (m, 1H), 7.20 (dd, 1H), 7.36 (d, 1H), 7.54 (s, 1H), 7.59 (d, 1H),7.73 (bs, 1H), 11.75 (s, 1H) ppm; LC-MS (ESI) 490 (M+H⁺-Cl), 526 (M+H⁺)

1.1o Synthesis of Compound 13c.

To a solution of Compound 12b (19 mg, 0.0387) in DMF (2 mL) were added5-(2-dimethylamino-ethoxy)-benzofuran-2-carboxylic acid HBr salt (25 mg,0.0775 mmole) and PS-carbodiimide (82 mg, mmole/g: 0.94, 0.0775 mmole).The reaction mixture was stirred at room temperature for 24 h. Afterfiltration, the filtrate was concentrated and the residue was dissolvedin H₂O/CH₃CN/TFA (2/0.75/0.25, 3 mL) and it was placed in freezer for 3h. The yellow solid was collected by filtration and dried to give thetitle compound (18 mg, 82%). LC-MS (ESI) 490 (M+H⁺-Br), 570 (M+H⁺), 572(M+H⁺+2)

1.1p Synthesis of Compound 14a.

To a suspension of Compound 13a (48 mg, 0.10 mmole) in dichloromethane(4 mL) were added p-nitrophenyl chloroformate (80 mg, 0.40 mmole) andtriethylamine (56 μL, 0.40 m mole) at ±78° C. The mixture was warmed upto room temperature slowly and the stirring was continued for additional30 mM. To the reaction mixture was added compoundN-Boc-N,N′-dimethylethylenediamine (166 mg, 0.80 mmole) and stirredovernight. The mixture was concentrated and the residue was purified byflash chromatography on silica gel with 1.25% methanol indichloromethane as eluent to give the title compound as a white solid(71 mg, 100%) ¹H NMR δ1.45-1.47 (m, 9H), 2.69 (s, 3H), 2.97 (s, 3H),3.14-3.34 (m, 4H), 3.81-3.92 (m, 8H), 4.38-4.47 (m, 3H), 4.70 (d, 1H),7.05 (dd, 1H), 7.11 (d, 1H), 7.45 (s, 1H), 7.48 (d, 1H), 7.99 (s, 1H),10.43 (s, 1H) ppm. LC-MS (ESI) 710 (M−H⁺)

1.1q Synthesis of Compound 14b.

To a suspension of Compound 13b (48 mg, 0.075 mmole) in dichloromethane(2 mL) were added 4-nitrophenyl chloroformate (80 mg, 0.4 m mole) andtriethylamine (40 mg, 0.4 m mole, 56 μL) at 0° C. The mixture was warmedup to room temperature and stirring was continued additional 6 h. Thesolvent was evaporated and the residue was washed with ether to give theintermediate. The intermediate was dissolved in dichloromethane (2 mL)and to the reaction solution were addedN-Boc-N,N′-dimethylethylenediamine (44 mg, 0.2 m mole) and triethylamine(20 mg, 0.2 mmole, 28 μL). The mixture thus obtained was stirred at roomtemperature overnight. The mixture was concentrated and the residue waspurified by HPLC on C-18 column with ammonium formate (20 mM, pH 7.0)and acetonitrile as eluent to give the title compound as white solid (31mg, 54%). LC-MS (ESI) 755 (M+H⁺)

1.1r Synthesis of Compound 14c.

To a suspension of Compound 13c (24 mg, 0.04 mmole) in CH₂Cl₂ (2 mL)were added p-nitrophenyl chloroformate (64 mg, 0.32 mmole) andtriethylamine (22 μL, 0.16 mmole) at 0° C. The reaction mixture thusobtained was stirred at room temperature for 18 h. To the reactionmixture was added N-Boc-N,N′-dimethylethylenediamine (94 mg, 0.50 mmole)and the stirring was continued for additional 50 min. The reactionmixture was concentrated and the residue was purified by flashchromatography on silica gel with 5% methanol in dichloromethane aseluent to give the title compound as white solid (28 mg, 83%). LC-MS(ESI) 490, 570, 684 (M+H⁺-Boc), 784 (M+H⁴), 805 (M+Na⁺), 722 (M+K⁺)

1.1s Synthesis of Compound 15a.

Compound 14a (70 mg, 0.10 m mole) was dissolved in trifluoroacetic acid(5 mL) and the mixture was stirred at room temperature for 30 min andconcentrated to dryness and the product (72 mg, 100%) was used in nextstep without further purification. HPLC showed it to be >95% pure. ¹HNMR δ 2.64 (s, 3H), 2.93 (s, 3H), 3.19 (s, 3H), 3.30 (t, 1H), 3.79 (s,3H), 3.85 (s, 3H), 3.81-3.85 (m, 1H), 4.27-4.49 (m, 3H), 4.59 (d, 1H),4.68 (d, 1H), 6.97 (dd, 1H), 7.03 (d, 1H), 7.38 (s, 1H), 7.41 (d, 1H),8.00 (br s, 1H), 10.61 (br s, 1H) ppm. LC-MS (ESI) 612 (M+H⁺), 634(M+Na⁺)

1.1t Synthesis of Compound 15b.

Compound 15b was prepared as described above for Compound 15a in 100%yield. ¹H NMR (CD₃OD) δ 2.69 (s, 3H), 2.76 (s, 3H), 2.83 (bs, 1H), 3.01(s, 6H), 3.08 (bs, 1H), 3.24 (bs, 2H), 3.42 (m, 2H), 3.63 (bs, 3H), 3.74(bs, 1H), 3.91 (s, 3H), 3.92 (m, 1H), 4.40 (bs, 2H), 4.57 (bs, 2H), 4.71(bs, 1H), 7.22 (bd, 1H), 7.36 (s, 1H), 7.56 (s, 1H), 7.59 (d, 1H), 8.04(bs, 1H) ppm; LC-MS (ESI) 490, 526, 640 (M+H⁺), 678 (M+K⁺).

1.1u Synthesis of Compound 15c.

Compound 15c was prepared as described above for Compound 15a in 100%yield. LC-MS (ESI) 490, 570, 684 (M+H⁺), 722 (M+K⁺)

1.1v Synthesis of Compound 16a.

To a solution of Compound 5 (12.5 mg, 0.019 mmole) and Compound 15a (10mg, 0.014) in dimethylformamide (200 μL) was added triethylamine (6 μL,0.044 mmole). The mixture thus obtained was stirred at room temperatureovernight. Ether (5 mL) was added to the mixture and a white solidprecipitated out of solution. The solid was filtered and purified byflash chromatography on silica gel with dichloromethane, followed by 1%methanol in dichloromethane, 2% methanol in dichloromethane, 3% methanolin dichloromethane and finally 4% methanol in dichloromethane as eluentto give the title compound as a white solid (8.7 mg, 56%). LC-MS (ESI)470, 1112 (M+H⁺), 1134 (M+Na⁺), 1150 (M+K⁺)

1.1w Synthesis of Compound 16b.

To a solution of Compound 15b (5 mg, 0.0056 mmole) in DMF (0.35 mL) wereadded Compound 5 (3.8 mg, 0.0056 mmole) and DIEA (2 μL, 0.011 mmole).The mixture thus obtained was stirred at room temperature for 5 h. Themixture was concentrated and the residue was purified by flashchromatography on silica gel with 10% methanol in dichloromethane aseluent to give the title compound as a solid (3 mg, 45%). LC-MS (ESI)490, 526, 1169 (M+H⁺), 1208 (M+K⁺)

1.1x Synthesis of Compound 16c.

Compound 16c was prepared as described above for Compound 16b in 50%yield. LC-MS (ESI) 490, 570, 1212 (M+H⁺), 1250 (M+K⁺)

1.1y Synthesis of Compound 17a.

To a solution of Compound 16a (8.7 mg, 0.008 mmole) in dimethylformamide(500 μL) was added piperidine (100 μL) in one portion. The mixture thusobtained was stirred for 20 minutes at room temperature. The solventwere removed on the rotovap, and placed on the high vacuum for 1.5 h.The residue was take up in the minimal amount of dichloromethane (100μL) and hexane (3 mL) was add to the solution, a white solid crashed outof solution which was filtered off and dried (6.7 mg, 96.7%). MS (ES)470, 890.1 (M+H⁺), 912 (M+Na⁺), 928 (M+K⁺).

1.1z Synthesis of Compound 17b.

Compound 17b was prepared as described above for Compound 17a in 95%yield. LC-MS (ESI) 947 (M+H⁺)

1.1aa Synthesis of Compound 17c.

Compound 17c was prepared as described above for Compound 17a in 95%yield. LC-MS (ESI) 1015 (M+H⁺)

1.1bb Synthesis of Compound 18a.

To a solution of Compound 17a (4.2 mg, 0.005 mmole) and Compound 3 (2.64mg, 0.005 mmole) in dichloromethane (1 mL) was added in one portionPyBOP (3.7 mg, 0.007 mmole) followed by diisopropylethylamine (1 μL).The mixture thus obtained was stirred overnight at room temperature. Thesolvents were removed on the rotovap. The residue was purified by PrepHPLC to yield a beige solid (2.6 mg, 38.7%). MS (ES) 470, 1431 (M+H⁺),1453 (M+Na⁺), 1469 (M+K⁺)

1.1cc Synthesis of Compound 18b.

To a solution of Compound 17b (2.2 mg, 0.0025 mmole) and Compound 3 in5% methanol in dichloromethane (400 μL) were added HBTU (9 mg, 0.0046mmole) and DIEA (1.4 μL, 0.0046 mmole). The mixture thus obtained wasstirred at room temperature overnight. The solvent was evaporated andthe residue was purified on semi-preparative HPLC with 10 mM ammoniumformate and acetonitrile as eluent to give the title compound as an oil(1.1 mg, 30%). LC-MS (ESI) 490, 526, 1488 (M+H⁺), 1527 (M+K⁺)

1.1 dd Synthesis of Compound 18c.

To a solution of Compound 17c (6.5 mg, 0.0065 mmole) and the Compound 3(5.5 mg, 0.0097 mmole) in 5% methanol in dichloromethane (0.5 mL) wereadded HBTU (3.7 mg, 0.0097 mmole) and DIEA (3.4 μL, 0.0194 m mole). Themixture thus obtained was stirred at room temperature overnight. Thesolvent was evaporated and the residue was purified by flashchromatography on silica gel with 30% methanol in dichloromethane aseluent to give the title compound as an oil (4 mg, 30%). LC-MS (ESI)1532 (M+H⁺), 1554 (M+Na⁺), 1570 (M+K⁺).

1.2 Synthesis Methodology for Duocarmycin-Containing Peptide Linkerwithout Self-Immolative Spacer

1.2a Reaction A:

To a suspension of Alkylating core 7 mg in 2 mL of Ethyl Acetate waspassed a slow stream of dry HBr gas until a clear solution is formedwhich took approximately 15 minutes. The reaction mixture wasconcentrated and dried overnight under high vacuum.

1.2b Reaction B:

To a suspension of the bromo methyl seco compound prepared in step A inDMF was added EDC (10 mg, 0.054 mMoles) and 5-Nitro benzofurancarboxylic acid (12 mg, 0.054 mMoles) and allowed to stir for 6 hours.To this reaction mixture was then added ethyl acetate and brine. Thecombined organic layers were concentrated after three extractions withethyl acetate. And filtered over silica gel using MeOH/DCM withincreasing amounts of MeOH The product was confirmed by Mass Spec,M+1=530

1.2c Reaction C:

The 4′-OH was protected using methyl piperazine carbonyl chloride (11mg, 0.054 mMoles) in 2 mL DCM, 200 μL Allyl alcohol and pyridine (21 μL)for 2 hours. The product was purified by silica gel columnchromatography and Identified by Mass Spec, MS+1=654

1.2d Reaction D:

Reduction of Nitro group was done by hydrogenolysis over Pd/C inDCM/MeOH (2:1) under 40 PSI for 45 minutes. The product was filtered andthe filtrate concentrated and dried under high vacuum. The product wasconfirmed by mass spec analysis MS+1=and carried out to the next stepwithout further purification.

1.2e Reaction E:

To a solution of above compound (18 mg, 0.024 mMoles) in MeOH/DCM (2:1,3 mL) was added Fmoc-Val-Citruline (29 mg, 0.06 mMoles) the resultantmixture was stirred for 10 minutes until all the acid dissolved. 15 mg,0.06 moles of EEDQ was added and the reaction mixture was stirred in thedark overnight. The reaction mixture was then concentrated, rinsed withdiethyl ether and the residue was purified by reverse phase Prep HPLC togive the product which was identified by Mass Spec M+1=1103.

1.2f Reaction F:

Deprotection of Fmoc protecting group was done using 5% piperidine in 1mL DMF for 10 minutes. Concentration of the reaction mixture wasfollowed by rinsing the solid residue with diethyl ether. Product wasconfirmed by Mass Spec, MS+1=880 and M+K=919

1.2g Reaction G:

To a solution of the free amine in DMF (1.5 mL) prepared in step F wasadded Mal-(PEG)₄-NHS-ester (20 mg) and the reaction mixture stirred for1 hr. Concentration followed by purification reverse phase Prep HPLCgave 2.8 mg of (11% overall yield, beginning from Alkylating core) whichwas confirmed by mass spec MS+1=2178, M+Na=1300 and M+K=1316

1.3 Synthesis of Peptide Linker Conjugated with Tubulysine A

The ligand can be linked to PEG and peptide linker by the synthesisshown.

The synthesis of intermediates and ligand-drug conjugate having apeptide linker where the drug is Tubulysine A is shown hereinabove. Thisbasic method may be used with other drugs.

1.4a Synthesis of Peptide-Linker Conjugate 111

1.4b Synthesis of Peptide-Linker Conjugate 112

1.4c Synthesis of Peptide-Linker Conjugate 113

Example 2 Synthesis of 6-Membered Hydrazine Linker Conjugates

2.1 Synthesis of a 6-Membered Gem-Dimethyl Hydrazine Linker Conjugatedto a Duocarmycin Derivative Cytotoxin

2.1a Synthesis Scheme for Compound 109

2.1b Synthesis of Compound 110

To a suspension of Cbz-dimethyl alanine (1 g, 3.98 mMoles) in 30 mL ofDCM at ice-bath temperature was added HOAT (catalytic, 0.25equivalents), DIPEA (2.8 mL, 16 mmoles) followed by2-chloro-1,3-dimethylimidazolidinium hexafluorophosphate (CIP) (1.2 g,4.4 mmoles). To this reaction mixture was then added Boc-NN(Me) (643moles, 4.4 mmoles). The reaction mixture was allowed to stir overnightat room temperature. To the reaction mixture is added 10% citric acidsolution (100 mL) and extracted with DCM. The organic phase was washedwith water and then with a saturated solution of sodiumbicarbonatefollowed by water again. The organic phase was then concentrated andpurified by silica gel column with increasing polarity of ethyl acetatein hexanes to give 860 mg, 57% yield 107 which identified by mass specM+1=380 and M+NH₄ ⁺=397.

The Cbz protecting group was removed by catalytic hydrogenation usingPd/C in MeOH to give compound 108 which was confirmed by MS.

To a solution of PNPC-1918 (10 mg, 0.1 mmoles) in 2 mL DCM was addeddrop wise a solution of Compound 108 (60 mg, 0.25 mmoles) in 8 mL of DCMand the reaction mixture was allowed to stir for 2 days till all thestarting material had disappeared. The reaction mixture was filteredthrough a short silica gel pad and then concentrated and purified byreverse phase Prep HPLC to give 4.2 mg of Compound 109. This wasidentified by Mass Spec M+1=740. Boc Deprotection of Compound 109 wasdone with pure TFA for 20 minutes to give Compound 110. The product wasidentified by Mass Spec, M+1=640.

2.1c Synthesis of Compound 111

The Mal-PEG₄-Acetophenone and compound 110 (3 mg, 0.005 mmoles) werecombined concentrated and dried overnight under high vacuum. To thismixture was added a 1 mL of 5% acetic acid solution prepared a dayearlier and dried over molecular sieves. The formation of hydrazone wascomplete in less then an hour. After which the reaction mixture wasconcentration and purified by reverse phase Prep HPLC (ammonium formatePh=7) to give 2.8 mg of compound III (60% yield). The product wasidentified by Mass Spec, MS+1=1129, M+NH₄=1146 and M+K=1168

2.2 Synthesis of a Gem-Dimethyl 6-Membered Hydrazine Linker Conjugatedto a Tubulysin Cytotoxin

Similar methodology as shown in Example 2.1 can be applied for thesynthesis of a geminal dimethyl 6-membered hydrazine linker complexedwith a drug such as tubulysin A is shown.

2.3 Synthesis of a Hydrazine Linker Conjugated to a Duocarmycin Analog

To a solution of the bromo methyl seco compound (0.074 mMoles) in 3 mLDMF was added the 5-actyl indole-2-carboxylate (30 mg, 0.15 mMoles) andEDC (28 mg, 0.15 mMoles) and the resulting mixture was stirredovernight. The reaction mixture was concentrated and purified by silicagel chromatography using 5% MeOH in DCM Tt give 29 mg (74% yield) ofproduct which was confirmed by mass spec M+1=523.

To a solution of the compound synthesized in step C in 5 mL DCM and 300μL allyl alcohol was added methyl piperazine carbonyl chloride (22 mg,0.11 m Moles) and pyridine 44 μL. The reaction mixture was stirred atroom temperature for 5 hours. Concentration followed by purification bysilica gel chromatography using 5% MeOH/DCM as eluant gave 48 mg of thedesired product (73% yield). The product was confirmed by Mass Spec.M+1=650.

A solution of the above compound (8.2 mg, 0.012 mmoles) andMal-PEG₄-hydrazine in 5% acetic acid in anhydrous DCM was stirred atroom temperature for 20 minutes followed by evaporation of Solvents andReverse phase Prep HPLC using acetonitrile and ammonium formate bufferedaqueous phase gave 2.5 mg of the desired final product which wasconfirmed by mass Spec, M+1=1063

2.4a Rate of Cyclization of a Dimethyl 6-Membered Hydrazine Linker

A duocarmycin analog conjugated to a dimethyl 6-membered hydrazinelinker was incubated in buffer at pH 7.4 for 24 hours and the generationof cyclized product resulting from cyclization of the hydrazine linker,thereby releasing free duocarmycin analog, was assessed over time.

Minimal amounts of cyclized product were detected over 24 hours atpH=7.4, indicating this form of 6-membered hydrazine linker exhibits arelatively slow rate of cyclization.

2.4b Rate of Cyclization of a Gem-Dimethyl 6-Membered Hydrazine Linker

A duocarmycin analog conjugated to a gem-dimethyl 6-membered hydrazinelinker was incubated in buffer at pH 7.4 and the generation of cyclizedproduct resulting from cyclization of the hydrazine linker, therebyreleasing free duocarmycin analog, was assessed over time.

With the 6-membered gem-dimethyl linker, the cyclization reaction wasquite rapid, proceeding to completion within a few minutes. Thus, therate of cyclization for the gem-dimethyl 6-membered hydrazine linkerproceeded at a much faster rate than that of the 6-membered linker thatdid not contain the gem-dimethyl moiety.

Example 3 Synthesis of 5-Membered Hydrazine Linker Conjugates

3.1 Synthesis Methodology for Compound 4

Cbz-DMDA-2,2-Dimethylmalonic Acid (1)

To a solution of 2,2-Dimethyl-malonic acid (2.0 gm, 0.0151 moles),Thionyl chloride (1.35 ml, 0.0182 moles) in THF (15 ml) in a 25 mL flaskequipped with a stir bar, temperature probe, and reflux condenser wasadded a drop of DMF and the reaction mixture was heated to reflux for 2hrs then cooled to room temperature. This reaction mixture wastransferred to drop wise to a solution of Cbz-DMDA (4 gm, 0.0182 moles)and triethylamine (4 ml, 0.0287 moles) in THF (5 ml) at 0 C and wasstirred for 30 min at this temperature. The solvent was removed in vacuoand the residue dissolved in 1N HCl (50 ml) and extracted with DCM (2×25ml). The combined organic layers were extracted with 1N NaOH (2×25 ml)and the combined aqueous layer were acidified (pH<1) with conc. HCl andextracted with EtOAc (2×25 ml), dried over MgSO₄, filtered andconcentrated in vacuo to an off-white sticky solid, 3.44 gm, 68% yield.Compound 1 was confirmed by mass spec: m/z 337.0 [M+1]⁺

HPLC retention time: 3.77 min (mass spec)

Cbz-DMDA-2,2-Dimethylmalonic-Boc-N′-methylhydrazine (2)

To a solution of Compound 1 (3.0 gm, 0.0089 moles), Thionyl chloride(0.78 ml, 0.0107 moles) in THF (25 ml) in a 50 ml 3N RBF equipped with astir bar, temperature probe, and reflux condenser was added a drop ofDMF and the reaction mixture was refluxed for 2 hrs then cooled to roomtemperature. This reaction mixture was then added dropwise to a solutionof Boc-N-methyl hydrazine (1.33 gm, 0.091 moles) and triethylamine (3ml, 0.0215 moles) in THF (25 ml) at 0 C and stirred for 30 min. Thesolvent was removed in vacuo and the residue dissolved in EtOAc (50 ml),dried over MgSO₄, filtered and concentrated in vacuo to a brown oil. Theoil was dissolved in EtOAc and purified by column chromatography (100%EtOAc) resulting in 3.45 gm, 83% yield of a clear oil. Compound 2 wasconfirmed by mass spec: m/z 465.2 [M+1] HPLC retention time: 3.97 min(mass spec)

DMDA-2,2-Dimethylmalonic-Boc N′-methylhydrazine (3)

To a solution of Compound 2 (0.5 gm, 0.0011 moles) in MeOH (30 ml) wasadded 10% Pd/C (15 mg) and the reaction placed on a Parr hydrogenatorfor 30 minutes. The catalyst was filtered off and filtrate concentratedin vacuo to a clear oil to yield Compound 3 (0.38 gm). Product wasconfirmed by NMR ('H, CDCl₃): δ 1.45 (s, 15H) 2.45 (s, 3H) 2.85 (s, 6H),3.16 (s, 3H) 4.64 (m, 1H) 10.6 (bs, 1H); NMR (13C, CDCl₃) δ 24.1, 28.57,35.15, 35.58, 36.66, 47.01, 48.51, 81.11, 155.17, 173.56, 176.24

Synthesis of Compound 4

To a 15 ml RBF equipped with a stir bar, was combined Compound 3 (50 mg,0.1513 mmoles), PNPC-1918 (20 mg, 0.0315 mmoles) and DCM (5 ml). Thesolution was stirred for 30 minutes, then triethylamine (25 uL, 0.1794mmoles) was added and the bright yellow solution was stirred for 1 hr.The solution was concentrated in vacuo to a yellow oil and purified bycolumn chromatography (100% DCM to 1:1 EtOAc/DCM) to yield Compound 4 asan off-white solid, 22 mg, (84%). Product was confirmed by mass spec:m/z 825.7 [M+1]⁺

HPLC retention time: 7.65 min (mass spec)

3.2 Synthesis of an Antibody-Drug Conjugate having a 5-MemberedHydrazine Linker

This scheme demonstrates the conjugation of an antibody to a linker-drugcomplex. These methodologies are well known in the pharmaceutical art.Examples of other reactive sites includes maleimides, haloacetamideswith thiols on a ligand, thiols that react with disulfides on a ligand,hydrazides that react with aldehydes and ketones on a ligand, andhydroxysuccinimides, isocynates, isothiocyanates, and anhydride thatreact with amino group on a ligand.

Example 4 Synthesis of Disulfide Membered Linker Conjugates

4.1a Synthesis of Compound 1.

To a flask containing PEG₄ (3.88 g, 20 mmole) was added triton B (40%solution in methanol, 1.08 mL, 0.25 mmole) and tert-butyl acrylate (3.62mL, 24 mmole) followed after 15 min. The mixture was stirred at roomtemperature overnight. The mixture was concentrated in vacuo and theresidue was purified by flash chromatography on silica gel with 1%methanol in dichloromethane as eluent to give the title compound as ancolorless oil (2.35 g, 36%). ¹H NMR δ 1.45 (s, 9H), 2.5 (t, 2H), 3.65(m, 18H).

4.1b Synthesis of Compound 2.

To a solution of Compound 1 (1.17 g, 3.6 mmole) in dichloromethane (10mL) were added triethylamine (532 μL, 4 mmole) and methanesulfonylchloride (309 μL, 4 mmole). The mixture thus obtained was stirred atroom temperature overnight. The solvent was evaporated and the residuewas purified by flash chromatography on silica gel with 1% methanol indichloromethane as eluent to give the title compound as an yellow oil(1.3 g, 89%). ¹H NMR δ 1.43 (s, 9H), 2.48 (t, 2H), 3.07 (s, 3H),3.62-3.70 (m, 14H), 3.76 (m, 2H), 4.37 (m, 2H).

4.1c Synthesis of Compound 3.

To a solution of Compound 2 (1.3 g, 3.25 mmole) in ethanol (10 mL) wasadded sodium azide (423 mg, 6.5 mmole). The mixture thus obtained wasrefluxed overnight. The solvent was evaporated and the residue waspurified by flash chromatography on silica gel with 1% methanol indichloromethane as eluent to give the title compound as an yellow oil(1.01 g, 90%). ¹H NMR δ 1.45 (s, 9H), 2.50 (t, 2H), 3.40 (t, 2H),3.62-3.73 (m, 16H).

4.1d Synthesis of Compound 4.

To a solution of Compound 3 (470 mg, 1.35 mmol) in ether (5 mL)containing H₂O (25 μL) was added triphenylphosphine (391 mg, 1.48mmole). The mixture thus obtained was stirred at room temperatureovernight. The solvent was evaporated and the residue was purified byflash chromatography on silica gel with 1% methanol in dichloromethaneas eluent to give the title compound as an yellow oil (325 mg, 75%). ¹HNMR δ 1.45 (s, 9H), 2.24 (bs, 2H), 2.51 (t, 2H), 2.91 (t, 2H), 3.56 (m,2H), 3.63-3.66 (m, 12H). 3.72 (m, 2H).

4.1e Synthesis of Compound 5.

To a solution of 3-mercaptopropionic acid (1.22 g, 11.5 mmole) inmethanol (10 mL) was added aldrithiol-2 (3.78 g, 17.25 mmole). Themixture thus obtained was stirred at room temperature for 3 hours. Thesolvent was evaporated and the residue was purified by flashchromatography on silica gel with 30% ethyl acetate in hexanes as eluentto give the title compound as an oil (2.44 g, 98%). ¹H NMR δ 2.8 (t,2H), 3.05 (t, 2H), 7.14 (m, 1H), 7.67 (m, 2H), 8.48 (m, 1H).

Compound 5b: ¹H NMR δ 1.43 (d, 3H), 2.61 (m, 1H), 2.76 (m, 1H), 3.40 (m,1H), 7.17 (m, 1H), 7.66 (m, 2H), 8.45 (m, 1H).

4.1f Synthesis of Compound 6.

3-Methyl benzothiazolium iodide (1 g, 3.6 mmole) was dissolved in 2 Nsodium hydroxide aqueous solution (10 mL) and the mixture was stirredfor 6 hours at 100° C. then acidified with 6 N hydrochloric acid aqueoussolution to pH 4 and extracted with diethyl ether. The organic layer wasdried over Na₂SO₄, rotary evaporated in vacuo and the residue wasdissolved in methanol (10 mL) and compound 5a (776 mg, 3.6 m mole) wasadded. The mixture was stirred at room temperature for 1 hour. Themixture was concentrated to dryness and the residue was purified byflash chromatography on silica gel with 1% methanol in dichloromethaneas eluent to give the title compound as a yellow oil (482 mg, 55%). ¹HNMR δ 2.85 (m, 2H), 2.95 (m, 5H), 6.64 (m, 2H), 7.3 (m, 1H), 7.4 (dd,1H); MS (ES) 244 (M+H⁺), 487 (2M+H⁺).

Compound 6b: ¹H NMR δ 1.35 (d, 3H), 2.48 (m, 1H), 2.92 (s, 3H), 3.02 (m,1H), 3.34 (m, 1H), 6.62 (m, 2H), 7.28 (m, 1H), 7.44 (m, 1H); MS (ES) 258(M+H⁺).

Compound 6c: ¹H NMR δ 1.45 (s, 6H), 2.70 (s, 2H), 2.93 (s, 3H), 6.62 (m,2H), 7.24 (m, 1H), 7.51 (m, 1H); MS (ES) 272 (M+H⁺), 294 (M+Na⁺), 310(M+K⁺).

4.1g Synthesis of Compound 7.

To a solution of Compound 6a (28 mg, 0.115 mmole) in anhydrous methanol(1 mL) was added acetyl chloride (13 μL, 0.173 mmole). The mixture thusobtained was stirred at room temperature overnight. The solvent wasevaporated and the residue was purified by flash chromatography onsilica gel with 10% ethyl acetate in hexanes as eluent to give the titlecompound as an oil (24 mg, 83%). ¹H NMR δ 2.08 (m, 2H), 2.93 (s, 3H),2.95 (m, 2H), 3.70 (s, 3H), 6.63 (m, 2H), 7.28 (m, 2H), 7.40 (m, 2H); MS(ES) 258 (M+H⁺), 280 (M+Na⁺), 296 (M+K⁺).

Compound 7b: ¹H NMR δ 1.32 (d, 3H), 2.45 (m, 1H), 2.92 (s, 3H), 2.93 (m,1H), 3.35 (m, 1H), 3.67 (s, 3H), 6.62 (m, 2H), 7.26 (m, 1H), 7.44 (m,1H); MS (ES) 272 (M+H⁺).

Compound 7c: ¹H NMR δ 1.42 (s, 6H), 2.66 (s, 2H), 2.93 (s, 3H), 3.62 (s,3H), 6.62 (m, 2H), 7.24 (m, 1H), 7.51 (m, 1H); MS (ES) 286 (M+H⁺), 308(M+Na⁺), 324 (M+K⁺).

4.1h Synthesis of Compound 8.

To a solution of Compound 7a (24 mg, 0.093 mmole) in dichloromethane (1mL) were added triphosgene (28 mg, 0.093 mmole) and triethylamine (37μL, 0.28 mmole) at 0° C. The mixture was stirred for 1 hour. The mixturewas concentrated to dryness and the residue was used in next stepwithout further purification.

The crude material was dissolved in dichloromethane (1 mL) and theCompound 8a (35 mg, 0.074 mmole), and DMAP (23 mg, 0.190 mmole) wereadded. The mixture thus obtained was stirred at room temperature forovernight. The solvent was evaporated and the residue was purified byflash chromatography on silica gel with 1% methanol in dichloromethaneas eluent to give the title compound as an yellow oil (53 mg, 76%). ¹HNMR δ 2.70 (s, 3H), 2.74 (m, 2H), 3.06 (m, 2H), 3.34 (m, 1H), 3.35 and3.36 (2s, 3H), 3.63 and 3.64 (2s, 3H), 3.86 (m, 1H), 3.88 (s, 3H), 3.93and 3.94 (2s, 3H), 4.48 (m, 1H), 4.55 (m, 1H), 4.79 (m, 1H), 7.05 (m,1H), 7.11 (m, 1H), 7.26-7.52 (m, 5H), 7.85 (d, 1H), 8.1 (bs, 1H), 8.98and 9.08 (2s, 1H); MS (ES) 753 (M+H⁺).

Compound 8b: ¹H NMR δ 1.38 (m, 3H), 2.52 (m, 1H), 2.69 (m, 3H), 2.79 (m,1H), 3.33 (m, 1H), 3.37 (2s, 3H), 3.64 (m, 3H), 3.88 (s, 3H), 3.84-3.90(m, 1H), 3.93 (2s, 3H), 4.48 (m, 1H), 4.57 (m, 1H), 4.78 (m, 1H), 7.06(m, 1H), 7.12 (m, 1H), 7.26-7.43 (m, 3H), 7.50 (m, 2H), 7.86 (m, 1H),8.1 (bs, 1H), 8.99, 9.08, 9.13 and 9.22 (4s, 1H); MS (ES) 767 (M+H⁺).

Compound 8c: ¹H NMR δ 1.44 (m, 6H), 2.63 (d, 2H), 2.70 (s, 3H), 3.35 (m,1H), 3.38 and 3.39 (2s, 3H), 3.63 and 3.64 (2s, 3H), 3.87 (m, 1H), 3.88(s, 3H), 3.93 and 3.94 (2s, 3H), 4.48 (m, 1H), 4.55 (m, 1H), 4.79 (m,1H), 7.05 (m, 1H), 7.12 (m, 1H), 7.31-7.39 (m, 3H), 7.49 (m, 2H), 7.89(d, 1H), 8.1 (bs, 1H), 9.12 and 9.23 (2s, 1H); MS (ES) 781 (M+H⁺).

4.1i Synthesis of Compounds 9 and 10.

To a solution of Compound 8a (0.1 mg) in PBS buffer solution (pH7.2)/methanol (300 μL, 2/1) was added a 20 mM solution of DTT (100 μL,15 equiv.) and monitored the progress of the reaction by HPLC. Thereaction underwent too fast to detect, after few seconds the reactionwas completed already to give product Compound 10 quantitatively. Thereaction intermediate Compound 9 was not detected.

4.1j Synthesis of Compound 11.

To a solution of Compound 6a (66 mg, 0.2 m mole) in dichloromethane (1mL) were added DCC (47 mg, 0.22 m mole), HOBt (31 mg, 0.22 mmole) andthe compound 4 (50 mg, 0.2 m mole). The mixture thus obtained wasstirred at room temperature overnight. The solvent was evaporated andthe residue was purified by flash chromatography on silica gel with 1%methanol in dichloromethane as eluent to give the title compound as anyellow oil (70 mg, 62%). ¹H NMR δ 1.44 (s, 9H), 2.51 (t, 1H), 2.63 (t,2H), 2.93 (d, 3H), 3.01 (t, 2H), 3.45 (m, 2H), 3.55 (m, 2H), 3.64 (m,12H), 3.71 (t, 2H), 5.01 (bs, 1H), 6.38 (bt, 1H), 6.62 (m, 2H), 7.27 (m,1H), 7.43 (dd, 1H). MS (ES) 491 (M-56+H⁺), 513 (M-56+Na⁺), 547 (M+H⁺),569 (M+Na⁺)

Compound 11b: ¹H NMR δ 1.34 (d, 3H), 1.45 (s, 9H), 2.30 (m, 1H), 2.5 (t,2H), 2.69 (m, 1H), 2.93 (d, 3H), 3.37-3.55 (m, 5H), 3.63 (m, 12H), 3.71(t, 2H), 4.99 (bs, 1H), 6.13 (bt, 1H), 6.62 (m, 2H), 7.25 (m, 1H), 7.48(dd, 1H). MS (ES) 505 (M-56+H⁺), 527 (M-56+Na⁺), 543 (M-56+K⁺), 561(M+H⁺), 583 (M+Na⁺).

Compound 11c: 1.43 (s, 3H), 1.45 (s, 9H), 2.46 (s, 2H), 2.5 (t, 2H),2.92 and 2.94 (2s, 3H), 3.33 (m, 2H), 3.47 (t, 2H), 3.63 (m, 12H), 3.70(t, 2H), 6.06 (bt, 1H), 6.63 (m, 2H), 7.25 (m, 1H), 7.54 (d, 1H); MS(ES) 519 (M-56+H⁺), 541 (M-56+Na⁺), 575 (M+H⁺), 597 (M+Na⁺).

4.1 k Synthesis of Compound 12:

To a suspension of Compound 11a (20 mg, 0.037 mmole) in dichloromethane(1 mL) were added triethylamine (15 μL, 0.11 mmole) and a solution of 2N phosgene in toluene (55 μL, 0.11 m mole) at 0° C. The mixture wasstirred at room temperature for 1 hour. The mixture was concentrated andthe residue was dissolved in dichloromethane (1 mL) and the compound 10(14 mg, 0.030 mmole) and DMAP (9 mg, 0.076 m mole) were added. Themixture thus obtained was stirred at room temperature overnight. Thesolvent was evaporated and the residue was purified by flashchromatography on silica gel with 1% methanol in dichloromethane aseluent to give the title compound as an yellow oil (23 mg, 74%). ¹H NMRδ 1.44 (s, 9H), 2.49 (t, 2H), 2.67 (m, 2H), 2.65 and 2.67 (2s, 3H), 3.07(m, 2H), 3.33 (s, 3H), 3.40 (m, 3H), 3.51 (m, 2H), 3.60 (m, 12H), 3.69(m, 2H), 3.87 (s, 3H), 3.92 (s, 3H), 3.93 (m, 1H), 4.52 (m, 2H), 4.78(m, 1H), 6.65, 6.74 and 6.97 (3bt, 1H), 7.06 (d, 1H), 7.12 (s, 1H),7.29-7.42 (m, 3H), 7.50 (m, 2H), 7.87 (d, 1H), 8.10 and 8.15 (2bs, 1H),9.79 and 9.58 (2s, 1H); MS (ES) 986 (M+H⁺−56), 1042 (M+H⁺).

Compound 12b: ¹H NMR δ 1.32 (m, 3H), 1.44 (s, 9H), 2.39 (m, 1H), 2.48(m, 2H), 2.60 (m, 1H), 2.67 and 2.69 (2s, 3H), 3.32 and 3.35 (2s, 3H),3.38-3.72 (m, 20H), 3.88 (s, 3H), 3.93 (s, 3H), 3.94 (m, 1H), 4.52 (m,2H), 4.77 (m, 1H), 6.53, 6.67 and 6.72 (3bt, 1H), 7.06 (d, 1H), 7.12 (s,1H), 7.29-7.39 (m, 3H), 7.49 (m, 2H), 7.88 (d, 1H), 8.12 and 8.25 (2bs,1H), 9.13, 9.36, 10.08 and 10.21 (4s, 1H); MS (ES) 1000 (M+H⁺-56), 1056(M+H⁺), 1078 (M+Na⁺), 1084 (M+K⁺).

Compound 12c: ¹H NMR δ 1.30-1.42 (m, 3H), 1.44 (s, 9H), 2.45-2.52 (m,4H), 2.69 and 2.72 (2s, 3H), 3.34 and 3.35 (2s, 3H), 3.39-3.72 (m, 19H),3.88 (s, 3H), 3.925 and 3.93 (2s, 3H), 3.94 (m, 1H), 4.53 (m, 2H), 4.80(m, 1H), 6.63 (m, 1H), 7.06 (dd, 1H), 7.13 (d, 1H), 7.25-7.39 (m, 3H),7.50 (m, 2H), 7.89 (d, 1H), 8.10 and 8.27 (2bs, 1H), 9.99 and 10.191(2s, 1H); MS (ES) 1014 (M+H⁺−56), 1070 (M+H⁺), 1108 (M+K⁺).

4.1l Synthesis of Compound 13.

Compound 12a (23 mg, 0.022 mmole) was dissolved in the solution oftrifluoroacetic acid and dichloromethane (1 mL, 1/1) and the mixture wasstirred at room temperature for 30 min and concentrated to give theproduct (21 mg, 100%) ¹H NMR δ 2.60 (t, 2H), 2.67 and 2.68 (2s, 3H),2.75 (m, 2H), 3.07 (m, 2H), 3.34 (s, 3H), 3.38-3.64 (m, 21H), 3.76 (t,2H), 3.88 (s, 3H), 3.92 (s, 3H), 3.93 (m, 1H), 4.53 (m, 2H), 4.78 (m,1H), 7.06 (d, 1H), 7.13 (s, 1H), 7.31-7.43 (m, 3H), 7.49 (m, 2H), 7.87(d, 1H), 8.10 and 8.15 (2bs, 1H), 9.44 and 9.65 (2s, 1H); MS (ES) 986(M+H⁺), 1008 (M+Na⁴), 1024 (M+K⁺).

Compound 13b: ¹H NMR δ 1.34 (m, 3H), 2.56 (m, 1H), 2.62 (m, 2H), 2.68(m, 3H), 2.8 (m, 1H), 3.35-3.36 (2s, 3H), 3.40-3.70 (m, 18H), 3.77 (t,2H), 3.88 (s, 3H), 3.93 and 3.95 (2s, 3H), 3.94 (m, 1H), 4.54 (m, 2H),4.79 (m, 1H), 7.07 (d, 2H), 7.13 (s, 1H), 7.30-7.42 (m, 3H), 7.49 (m,2H), 7.88 (d, 1H), 8.11 and 8.25 (2bs, 1H), 9.22, 9.37, 9.80 and 9.92(4s, 1H); MS (ES) 1000 (M+H⁺), 1022 (M+Na⁺), 1038 (M+K⁺).

Compound 13c: ¹H NMR δ 1.30-1.45 (m, 6H), 2.54 (m, 2H), 2.61 (m, 2H),2.68 and 2.69 (2s, 3H), 3.35-3.36 (2s, 3H), 3.40-3.70 (m, 17H), 3.77 (t,2H), 3.88 (s, 3H), 3.92 and 3.93 (2s, 3H), 3.94 (m, 1H), 4.50 (m, 2H),4.80 (m, 1H), 7.08 (m, 2H), 7.12 (d, 1H), 7.29-7.39 (m, 3H), 7.49 (m,2H), 7.89 (m, 1H), 8.10 and 8.25 (2bs, 1H), 9.88 and 10.04 (2s, 1H); MS(ES) 1014 (M+H⁺), 1036 (M+Na⁺), 1054 (M+K⁺).

4.1m Synthesis of Compound 14a.

To a solution of Compound 13a (5.4 mg, 0.0054 mmole) in dichloromethane(1 mL) were added PS-carbodiimide (11.5 mg, 0.94 mmole/g, 0.0108 mmole),and PS-DMAP (7.2 mal 1.49 m mole/g, 0.0108 m mole). The mixture thusobtained was stirred at room temperature overnight, filtrated andconcentrated to give the product. MS (ES) 1082 (M+H⁺).

4.2 Synthesis of Disulfide Linker Conjugated with Tubulysin A

The drug Tubulysin A can be conjugated to the disulfide linker of thecurrent invention using the mechanism shown hereinabove. Other drugs andother linkers of the current invention can be synthesized using similarreaction schemes.

4.3 Rate of Cyclization of a Disulfide Linker

To a solution of Compound 8a (0.1 mg) in PBS buffer solution (pH7.2)/methanol (300 μL, 2/1) was added a 20 mM solution of DTT (100 μL,15 equiv.) and the progress of the reaction was monitored by HPLC. Thereaction underwent rapid cyclization, with the reaction being completedwithin a few seconds to give product 10 quantitatively. The reactionintermediate 9 was not detected.

Example 5

Synthesis of Compound 32.

To a solution of Compound 30 (120 mg, 0.28 mmole) in ethyl acetate (10mL) was bubbled HCl gas for 5 min. The reaction mixture was stirred atRT for another 30 min and then the mixture was concentrated. Ether wasadded to the reaction mixture and the white precipitate was collected ona filter funnel. Solid was dried overnight under vacuum to give 100 mgof the desired product which was confirmed by LC-MS (ESI) 324 (M+H⁺) andused in next step without further purification. To a solution of thiscompound (100 mg, 0.24 mmole) in DMF (5 mL) were added compound 31 (65mg, 0.26 mmole), HATU (100 mg, 0.26 mmole) and TEA (91 uL, 0.52 mmole).The mixture thus obtained was stirred at room temperature for 3 hrs. Thesolvent was evaporated and the residue was purified on semi-preparativeHPLC with 0.1% TFA in water and acetonitrile as eluent to give compound32 as an oil (110 mg, 80%). The desired product was confirmed by LC-MS(ESI) 555 (M+H⁺).

Synthesis of Compound 33.

A solution of Compound 32 (110 mg, 0.2 mmole) and palladium on charcoal(20 mg) in DCM (10 mL) and methanol (5 mL) was stirred under hydrogenatmospheric pressure at room temperature for 12 hrs. The palladium wasfiltrated and the reaction mixture was concentrated and the residue waspurified on semi-preparative HPLC with 0.1% TFA in water andacetonitrile as eluent to give the desired compound as an oil (80 mg,78%) LC-MS (ESI) 465 (M+H⁺). To a solution of the residue (80 mg, 0.17mmole) in dichloromethane (10 mL) and THF (5 mL) was added PNPCl(4-nitrophenyl chloroformate) (137 mg, 0.68 mmole) and triethyl amine(144 uL, 1.02 mmol) at 0° C. The mixture thus obtained was stirred for30 min at 0° C. and then at room temperature for 12 hrs. The reactionmixture was concentrated under vacuum, and the residue was precipitatedusing ethyl ether (100 mL) to give compound 33 as a yellow solid (90 mg,82%) which was dried under vacuum and confirmed by LC-MS (ESI) 631(M+H⁺).

Synthesis of Compound 34:

To a solution of 2-bromoethylamine bromide (5 g, 24.4 mmole) in DMF (50mL) was added diisopropylethylamine (8.5 mL, 48.8 mmole) and benzylchloroformate (3.48 mL, 24.4 mmole). The mixture thus obtained wasstirred at room temperature for 2 hours. The reaction mixture wasconcentrated and the residue was purified by flash chromatography onsilica gel with ethyl acetate/hexanes (3/7) as eluent to give thedesired compound 34 as an oil (4 g, 64%). ¹H NMR (CDCl₃)±3.54 (bs, 2H),3.61 (bs, 2H), 5.12 (s, 2H), 7.36 (m, 5H).

Synthesis of Compound 35:

To a solution of Compound 34 (3.34 g, 12.99 mmole) and valine tert-butylester (3.27 g, 15.59 mmole) in DMF (50 mL) was added potassium carbonate(5.39 g, 38.97 mmole) and potassium iodide (2.59 g, 15.59 mmole). Themixture thus obtained was stirred at 100° C. overnight. The reactionmixture was concentrated and the residue was purified by flashchromatography on silica gel with ethyl acetate/hexanes (2/8) as eluentto give the desired compound 35 as an oil (3.12 g, 69%). ¹H NMR (CDCl₃)δ 0.92 (m, 6H), 1.46 (s, 9H), 1.86 (m, 1H), 2.53 (m, 1H), 2.80 (m, 2H),3.18 (m, 1H), 3.31 (m, 1H), 5.10 (s, 2H), 5.25 (bs, 1H), 7.36 (m, 5H);LC-MS (ESI) 296 (M+H-tbutyl⁺), 352 (M+H⁺).

Synthesis of Compound 36.

A solution of Compound 35 (3.4 g, 9.72 mmole) and palladium on charcoal(200 mg) in methanol (30 mL) was placed under hydrogen atmosphericpressure at room temperature. The mixture thus obtained was stirred atroom temperature for 2 hours. The palladium was filtrated and thereaction mixture was concentrated to dryness to give the desiredcompound 36 as an oil (2.1 g, 98%)

Synthesis of Compound 37.

To a solution of Compound 36 (2.1 g, 9.72 mmole) in dichloromethane (30mL) was added FmocOSu (9-fluorenylmethoxycarbonyl-N-hydroxysuccinimideester) (3.28 g, 9.72 mmole) at 0° C. The mixture thus obtained wasstirred for 2 hours at 0° C. The solvent were removed on the rotovap,and the residue was purified by flash chromatography on silica gel withdichloromethane, followed by 0.5% methanol in dichloromethane andfinally 1% methanol in dichloromethane as eluent to give the desiredcompound 37 as colorless oil (2.55 g, 60%). ¹H-NMR (CDCl₃) δ 0.95 (ft,6H), 1.48 (s, 9H), 1.90 (m, 1H), 2.55 (m, 1H), 2.82 (m, 2H), 3.18 (m,1H), 3.32 (m, 1H), 4.24 (m, 1H), 4.37 (m, 2H), 5.40 (bs, 1H), 7.30 (m,2H), 7.39 (m, 2H), 7.60 (d, 2H), 7.75 (d, 2H) ppm; LC-MS (ESI) 383(M+H-tbutyl⁺), 440 (M+H⁺), 462 (M+Na⁺), 478 (M+K⁺).

Synthesis of Compound 38.

To a solution of Compound 37 (177 mg, 0.4 mmole) intetrahydrofuran-water (3/1, 8 mL) was bubbled HCl gas for 5 min. Thereaction mixture was stirred at 37° C. overnight then the mixture wasconcentrated to dryness to give the desired compound 38 as solid (168mg, 98%) which was confirmed by LC-MS (ESI) 383 (M+H⁺), 405 (M+Na⁺) andused in next step without further purification. LC-MS (ESI) 383 (M+H⁺),405 (M+Na⁺).

Synthesis of Compound 39.

To a solution of Compound 5 (525 mg, 0.79 mmole) in DMF (5 mL) was addedN-Boc-N,N′-dimethylethylenediamine (177 mg, 0.94 mmole). The mixturethus obtained was stirred at room temperature for 30 min. The solventwas removed and the residue was purified by flash chromatography onsilica gel with dichloromethane, followed by 2% methanol indichloromethane and finally 5% methanol in dichloromethane as eluent togive the desired compound 39 as colorless oil (364 mg, 65%). ¹H-NMR(CD₃OD) δ 1.39 (s, 9H), 1.56 (m, 2H), 1.70 (m, 1H), 1.82 (m, 1H), 2.70and 2.82 (2s, 3H), 2.90 (s, 3H), 3.09 (m, 1H), 3.17 (m, 1H), 3.30 to3.37 (m, 4H), 4.16 (t, 1H), 4.27 (m, 1H), 4.33 (d, 2H), 5.02 (bs, 2H),7.24 to 7.36 (m, 6H), 7.51 to 7.65 (m, 4H), 7.74 (d, 2H) ppm; LC-MS(ESI) 618 (M+H-Boc⁺), 662 (M+H-tbutyl⁺), 718 (M+H⁺), 740 (M+Na⁺), 1435(2M+H⁺).

Synthesis of Compound 40.

Compound 40 was prepared as described above for Compound 17a in 98%yield. LC-MS (ESI) 396 (M+H-Boc⁺), 496 (M+H⁺), 517 (M+Na⁺), 533 (M+K⁺),992 (2M+H⁺).

Synthesis of Compound 41.

To a solution of Compound 40 (138 mg, 0.28 mmole) in DMF (4 mL) wereadded the Compound 38 (110 mg, 0.28 mmole), HOBt (36 mg, 0.28 mmole) andEDC (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (50 mg,0.28 mmole). The mixture thus obtained was stirred at room temperatureovernight. The solvent was evaporated and the residue was purified onsemi-preparative HPLC with 0.1% TFA in water and acetonitrile as eluentto give the desired compound 41 as an oil (178 mg, 70%). ¹H-NMR (CD₃OD)δ 1.04 and 1.11 (2d, 6H), 1.40 (s, 9H), 1.58 (m, 2H), 1.77 (m, 1H), 1.88(m, 1H), 2.24 (m, 1H), 2.72 and 2.84 (2s, 3H), 2.92 (s, 3H), 3.10 to3.18 (m, 4H), 3.35 to 3.46 (m, 6H), 3.82 (d, 1H), 4.22 (t, 1H), 4.41 (m,2H), 4.59 (m, 1H), 5.04 (bs, 2H), 7.28 to 7.40 (m, 6H), 7.55 (m, 2H),7.63 (m, 2H), 7.78 (d, 2H) ppm; LC-MS (ESI) 760 (M+H-Boc⁺), 804(M+H-tbutyl⁺), 860 (M+H⁺), 882 (M+Na⁺), 899 (M+K⁺).

Synthesis of Compound 42.

Compound 42 was prepared as described above for Compound 17a in 98%yield. LC-MS (ESI) 538 (M+H-Boc⁺), 582 (M+H-tbutyl⁺), 638 (M+H⁺), 660(M+Na⁺).

Synthesis of Compound 43.

To a solution of Compound 42 (23 mg, 0.036 mmole) in dichloromethane (1mL) were added GMBS (N-(maleimidobutyryloxy)succinimide ester) (14 mg,0.05 mmole) and diisopropylethylamine (8.4 μL, 0.05 mmole) at 0° C. Themixture was warmed up to room temperature slowly and the stirring wascontinued for additional 30 min. The solvent was evaporated and theresidue was purified on semi-preparative HPLC with 0.1% TFA in water andacetonitrile as eluent to give the desired compound 43 as an oil (26 mg,79%). ¹H-NMR (CD₃OD) δ 1.06 and 1.12 (2d, 6H), 1.41 (s, 9H), 1.59 (m,2H), 1.78 (m, 1H), 1.86 to 1.93 (m, 3H), 2.24 (m, 3H), 2.74 and 2.84(2s, 3H), 2.93 (bs, 3H), 3.13 to 3.22 (m, 4H), 3.40 to 3.60 (m, 8H),3.82 (d, 1H), 4.60 (m, 1H), 5.05 (bs, 2H), 6.80 (s, 2H), 7.32 (m, 2H),7.57 (d, 2H), 8.78 (d, 1H) ppm; LC-MS (ESI) 703 (M+H-Boc⁺), 747(M+H-tbutyl⁺), 803 (M+H⁺), 825 (M+Na⁺), 841 (M+K⁺).

Synthesis of Compound 44.

Compound 44 was prepared as described above for Compound 15a in 98%yield. LC-MS (ESI) 703 (M+H⁺), 725 (M+Na⁺).

Synthesis of Compound 45.

To a solution of Compound 44 (15 mg, 0.016 mmole) and Compound 33 (10mg, 0.016 mmole) in DMF (0.8 mL) was added diisopropylethylamine (5.5μL, 0.032 mmole) at room temperature. The mixture thus obtained wasstirred at room temperature overnight. The solvent was evaporated andthe residue was purified on semi-preparative HPLC with 0.1% TFA in waterand acetonitrile as eluent to give the desired compound 45 as an oil (10mg, 45%). ¹H-NMR (CD₃OD) δ 1.02 to 1.13 (m, 6H), 1.55 (m, 2H), 1.74 (m,1H), 1.84 to 1.92 (m, 3H), 2.20 to 2.27 (m, 3H), 2.95 to 3.14 (m, 16H),3.47 to 3.84 (m, 12H), 3.98 (m, 1H), 4.2 to 4.34 (m, 3H), 4.57 (m, 1H),4.69 (m, 2H), 5.07 to 5.17 (m, 2H), 6.78 (s, 2H), 7.16 to 7.23 (m, 3H),7.30 (m, 1H), 7.38 to 7.47 (m, 3H), 7.52 to 7.58 (m, 3H), 7.81 to 7.92(m, 2H), 8.25 (bs, 1H) ppm; LC-MS (ESI) 1194 (M+H⁺), 1215 (M+Na⁺), 1233(M+K⁺).

Example 6

Synthesis of Compound (2).

A solution of 1 (100 mg, 0.24 mmol) and 10% Pd—C (35 mg) in MeOH/CH₂Cl₂(1/2, 10 ml) was degassed in vacuo for 40 s. The resulting mixture wasplaced under an atmosphere of hydrogen and stirred at 25° C. for 7 h.The reaction mixture was filtered through Celite (CH₂Cl₂ wash). Thesolvent was removed in vacuo. Chromatography on silica gel eluted withEtOAc/Hex (2/8) afforded 2 (77 mg, 98%). ¹NMR DMSO-d₆) δ 10.36 (s, 1H),8.04 (d, 1H, J=8.2 Hz), 7.72 (d, 1H, J=8.2 Hz), 7.61 (br s, 1H), 7.45(t, 1H, J=8.4 Hz), 7.261 (t, 1H, J=8.4 Hz), 4.06 (m, 4H), 3.73 (m, 1H),1.52 (s, 9H).

Synthesis of Compound (4).

A solution of 2 (35 mg, 0.1 mmol) in 4 M HCl-EtOAc (5 ml) was stirred at25° C. under Ar for 30 min. The solvent was removed in vacuo. To theresidue was added 5-acetylindone-2-carboxylic acid (24.4 mg, 0.12 mmol).A solution of EDC (22.9 mg, 0.12 mmol) in DMF (3 ml) was added and thereaction mixture was stirred at 25° C. for 5 h. The solvent was removed.The crude product was chromatographed on silica gel eluted with 10% MeOHin CH₂Cl₂ to give 4 (40.7 mg, 93%). ¹HNMR DMSO-d₆) δ12.13 (s, 1H), 10.47(s, 1H), 8.45 (s, 1H), 8.10 (d, 1H, J=8.4 Hz), 7.96 (br s, 1H), 7.85 (d,2H, J=8.4 Hz), 7.54 (d, 1H, J=8.4 Hz), 7.51 (t, 1H, J=8.2 Hz), 7.36 (t,1H, J=7.6), 7.35 (s, 1H), 4.81 (t, 1H, 11.2 Hz), 4.54 (dd, 1H, 8.8 Hz),4.23 (m, 1H), 4.01 (dd, 1H, J=10.2 Hz), 3.86 (dd, 1H, J=10.7 Hz), 2.61(s, 3H).

Synthesis of Compound (5).

4-Methyl-1-piperazinecarbonyl chloride hydrochloride (19.9 mg, 0.1 mmol)was added to a solution of 4 (20 mg, 0.05 mmol) and anhydrous pyridine(25 μml, 0.3 mmol) in 3% allyl alcohol in dry methylene chloride (4 ml)and the mixture was stirred for 16 h. Purification of the crude producton silica gel yielded 5 (23.6 mg, 91%). ¹NMR DMSO-d₆) δ 12.03 (s, 1H),8.41 (s, 1H), 8.21 (s, 1H), 8.01 (d, 1H, J=8.4 Hz), 7.88 (d, 1H, J=8.4Hz), 7.82 (dd, 1H, J=8.4 Hz), 7.58 (t, 1H, J=8.1 Hz), 7.51 (d, 1H, J=8.4Hz), 7.46 (t, 1H, J=7.6 Hz), 7.37 (s, 1H), 4.86 (t, 1H, J=10.8 Hz), 4.57(dd, 1H, J=10.8 Hz), 4.38 (m, 1H), 4.06 (dd, 1H, J=10.8 Hz), 3.86 (dd,1H, J=11 Hz), 3.41 (br, 4H), 3.29 (br, 4H), 2.82 (s, 3H), 2.57 (s, 3H).

Synthesis of Compound (7).

A solution of 5 (13 mg, 24 umol) and linker 6 (16.9 mg, 31 umol) in 5%acetic acid in dry methylene chloride (1 ml) was stirred for 30 min at25° C. The solvent was completely removed in vacuo and purified by HPLC(SymmetryPrep C₁₈, 7 μm, 19×150 mm column) to give 7 (18.5 mg, 81%). MS:calcd for C₄₈H₅₇ClN₈O₁₁ (M+H) m/z 958.38. found 958.10.

Example 7 Proliferation Assays

The biological activity of the cytotoxic compounds of the invention canbe assayed using the well established ³H-thymidine proliferation assay.This is a convenient method for quantitating cellular proliferation, asit evaluates DNA synthesis by measuring the incorporation of exogenousradiolabeled ³H-thymidine. This assay is highly reproducible and canaccommodate large numbers of compounds.

To carry out the assay, promyelocytic leukemia cells, HL-60, arecultured in RPMI media containing 10% heat inactivated fetal calf serum(FCS). On the day of the study, the cells are collected, washed andresuspended at a concentration of 0.5×10⁶ cells/ml in RPMI containing10% FCS. 100 μl of cell suspension is added to 96 well plates. Serialdilutions (3-fold increments) of doxorubicin (as a positive control) ortest compounds are made and 100 μl of compounds are added per well.Finally 10 μl of a 100 μCi/ml³H-thymidine is added per well and theplates are incubated for 24 hours. The plates are harvested using a 96well Harvester (Packard Instruments) and counted on a Packard Top Countcounter. Four parameter logistic curves are fitted to the ³H-thymidineincorporation as a function of drug molarity using Prism software todetermine IC₅₀ values.

The compounds of the invention generally have an IC₅₀ value in the aboveassay of from about 1 pM to about 100 nM, preferably from about 10 pM toabout 10 nM.

Example 8 Conjugation of Drug-Linker Molecules to Antibodies

This example describes reaction conditions and methodologies forconjugating a drug-linker molecule of the invention (optionallyincluding other groups, such as spacers, reactive functional groups andthe like) to an antibody as a targeting agent, X⁴. The conditions andmethodologies are intended to be exemplary only and non-limiting. Otherapproaches for conjugating drug-linker molecules to antibodies are knownin the art.

The conjugation method described herein is based on introduction of freethiol groups to the antibody through reaction of lysines of the antibodywith 2-iminothiolane, followed by reaction of the drug-linker moleculewith an active maleimide group. Initially the antibody to be conjugatedwas buffer exchanged into 0.1M phosphate buffer pH 8.0 containing 50 mMNaCl, 2 mM DTPA, pH 8.0 and concentrated to 5-10 mg/ml. Thiolation wasachieved through addition of 2-iminothiolane to the antibody. The amountof 2-iminothiolane to be added was determined in preliminary experimentsand varies from antibody to antibody. In the preliminary experiments, atitration of increasing amounts of 2-iminothiolane was added to theantibody, and following incubation with the antibody for one hour atroom temperature, the antibody was desalted into 50 mM HEPES buffer pH6.0 using a Sephadex G-25 column and the number of thiol groupsintroduced determined rapidly by reaction with dithiodipyridine (DTDP).Reaction of thiol groups with DTDP results in liberation of thiopyridinewhich is monitored at 324 nm. Samples at a protein concentration of0.5-1.0 mg/ml were used. The absorbance at 280 nm was used to accuratelydetermine the concentration of protein in the samples, and then analiquot of each sample (0.9 ml) was incubated with 0.1 ml DTDP (5 mMstock solution in ethanol) for 10 minutes at room temperature. Blanksamples of buffer alone plus DTDP were also incubated alongside. After10 minutes, absorbance at 324 nm was measured and the number of thiolspresent quantitated using an extinction coefficient for thiopyridine of19800M⁻¹.

Typically a thiolation level of three thiol groups per antibody isdesired. For example, with one particular antibody this was achievedthrough adding a 15 fold molar excess of 2-iminothiolane followed byincubation at room temperature for 1 hour. Antibody to be conjugated wastherefore incubated with 2-iminothiolane at the desired molar ratio andthen desalted into conjugation buffer (50 mM HEPES buffer pH 6.0containing 5 mM Glycine, 3% Glycerol and 2 mM DTPA). The thiolatedmaterial was maintained on ice whilst the number of thiols introducedwas quantitated as described above.

After verification of the number of thiols introduced, the drug-linkermolecule containing an active maleimide group was added at a 3-foldmolar excess per thiol. The conjugation reaction was carried out inconjugation buffer also containing a final concentration of 5% ethyleneglycol dimethyl ether (or a suitable alternative solvent). Commonly, thedrug-linker stock solution was dissolved in 90% ethylene glycol dimethylether, 10% dimethyl sulfoxide. For addition to antibody, the stocksolution can be added directly to the thiolated antibody, which hasenough ethylene glycol dimethyl ether added to bring the finalconcentration to 5%, or pre-diluted in conjugation buffer containing afinal concentration of 10% ethylene glycol dimethyl ether, followed byaddition to an equal volume of thiolated antibody.

The conjugation reaction was incubated at room temperature for 2 hourswith mixing. Following incubation the reaction mix was centrifuged at14000 RPM for 15 minutes and the pH was adjusted to 7.2 if purificationwas not immediate. Purification of conjugate was achieved throughchromatography using a number of methods. Conjugate can be purifiedusing size-exclusion chromatography on a Sephacryl 5200 columnpre-equilibrated with 50 mM HEPES buffer pH 7.2 containing 5 mM glycine,50 mM NaCl and 3% glycerol. Chromatography was carried out at a linearflow rate of 28 cm/h. Fractions containing conjugate were collected,pooled and concentrated. Alternatively purification can be achievedthrough ion-exchange chromatography. Conditions vary from antibody toantibody and need to be optimized in each case. For example,antibody-drug conjugate reaction mix was applied to an SP-Sepharosecolumn pre-equilibrated in 50 mM HEPES, 5 mM Glycine, 3% glycerol, pH6.0. The antibody conjugate was eluted using a gradient of 0-1 M NaCl inequilibration buffer. Fractions containing the conjugate were pooled,the pH was adjusted to 7.2 and the sample concentrated as required.

Each of the patent applications, patents, publications, and otherpublished documents mentioned or referred to in this specification isherein incorporated by reference in its entirety, to the same extent asif each individual patent application, patent, publication, and otherpublished document was specifically and individually indicated to beincorporated by reference.

While the present invention has been described with reference to thespecific embodiments thereof, it should be understood by those skilledin the art that various changes may be made and equivalents may besubstituted without departing from the true spirit and scope of theinvention and the appended claims. In addition, many modifications maybe made to adapt a particular situation, material, composition ofmatter, process, process step or steps, to the objective, spirit andscope of the present invention. All such modifications are intended tobe within the scope of the claims appended hereto.

1. A compound of the formula

wherein D is a drug moiety comprising a structure:

wherein the ring system A is a member selected from substituted andunsubstituted aryl, substituted and unsubstituted heteroaryl, andsubstituted and unsubstituted heterocycloalkyl groups; E and G aremembers independently selected from H, substituted and unsubstitutedalkyl, substituted and unsubstituted heteroalkyl, a heteroatom, a singlebond, or E and G are joined to form a ring system selected fromsubstituted and unsubstituted aryl, substituted and unsubstitutedheteroaryl, and substituted and unsubstituted heterocycloalkyl; X is amember selected from O, S and NR²³; R²³ is a member selected from H,substituted and unsubstituted alkyl, substituted and unsubstitutedheteroalkyl, and acyl; R³ is a member selected from the group consistingof (═O), SR¹¹, NHR¹¹ and OR¹¹, wherein R¹¹ is a member selected from thegroup consisting of H, substituted alkyl, unsubstituted alkyl,substituted heteroalkyl, unsubstituted heteroalkyl, diphosphates,triphosphates, acyl, C(O)R¹²R¹³, C(O)OR¹², C(O)NR¹²R¹³, P(O)(OR¹²)₂,C(O)CHR¹²R¹³, SR¹² and SiR¹²R¹²R¹⁴, in which R¹², R¹³, and R¹⁴ aremembers independently selected from H, substituted and unsubstitutedalkyl, substituted and unsubstituted heteroalkyl and substituted andunsubstituted aryl, wherein R¹² and R¹³ together with the nitrogen orcarbon atom to which they are attached are optionally joined to form asubstituted or unsubstituted heterocycloalkyl ring system having from 4to 6 members, optionally containing two or more heteroatoms; R⁴, R^(4′),R⁵ and R^(5′) are members independently selected from the groupconsisting of H, substituted alkyl, unsubstituted alkyl, substitutedaryl, unsubstituted aryl, substituted heteroaryl, unsubstitutedheteroaryl, substituted heterocycloalkyl, unsubstitutedheterocycloalkyl, halogen, NO₂, NR¹⁵R¹⁶, NC(O)R¹⁵, OC(O)NR¹⁵R¹⁶,OC(O)OR¹⁵, C(O)R¹⁵, SR¹⁵, OR¹⁵, CR¹⁵═NR¹⁶, and O(CH₂)_(n) N(CH₃)₂wherein n is an integer from 1 to 20; R¹⁵ and R¹⁶ are independentlyselected from H, substituted and unsubstituted alkyl, substituted andunsubstituted heteroalkyl, substituted and unsubstituted aryl,substituted and unsubstituted heteroaryl, substituted and unsubstitutedheterocycloalkyl, and substituted and unsubstituted peptidyl, whereinR¹⁵ and R¹⁶ together with the nitrogen atom to which they are attachedare optionally joined to form a substituted or unsubstitutedheterocycloalkyl ring system having from 4 to 6 members, optionallycontaining two or more heteroatoms; R⁶ is a single bond which is eitherpresent or absent and when present R⁶ and R⁷ are joined to form acyclopropyl ring; and R⁷ is CH₂—X¹ or —CH₂— joined in said cyclopropylring with R⁶, wherein X¹ is a leaving group, wherein at least one ofR¹¹, R¹², R¹³, R¹⁵ or R¹⁶, links said drug moiety D to L¹, if present,or to —C(O)—; each AA¹ is independently selected from the groupconsisting of natural amino acids and unnatural α-amino acids; c is aninteger from 1 to 20; L² is a substituted alkyl, unsubstituted alkyl,substituted heteroalkyl, unsubstituted heteroalkyl, unsubstitutedheterocycloalkyl, substituted heterocycloalkyl, substituted andunsubstituted aryl, and substituted and unsubstituted heteroaryl; L¹ isa self-immolative linker; m is an integer 0, 1, 2, 3, 4, 5, or 6; o is 0or 1; L⁴ is selected from substituted alkyl, unsubstituted alkyl,substituted aryl, unsubstituted aryl, substituted heteroalkyl, andunsubstituted heteroalkyl, any of which may be straight, branched, orcyclic; positively and negatively charged amino acid polymers; apolymer; and combinations thereof, wherein L⁴ does not comprise acarboxylic acyl group directly attached to the N-terminus of (AA¹)_(c);p is 1; and X⁴ is a member selected from the group consisting ofprotected reactive functional groups, unprotected reactive functionalgroups, detectable labels, and targeting agents.
 2. The compound ofclaim 1, wherein o is 1 and -(AA¹)_(c)-(L²)—C(O)— has the structure:

wherein R²⁴ is selected from the group consisting of H, substitutedalkyl, unsubstituted alkyl, substituted heteroalkyl, and unsubstitutedheteroalkyl; each K is a member independently selected from the groupconsisting of substituted alkyl, unsubstituted alkyl, substitutedheteroalkyl, unsubstituted heteroalkyl, substituted aryl, unsubstitutedaryl, substituted heteroaryl, unsubstituted heteroaryl, substitutedheterocycloalkyl, unsubstituted heterocycloalkyl, halogen, NO₂, NR²¹R²²,NR²¹COR²², OCONR²¹R²², OCOR²¹, and OR²¹; wherein R²¹ and R²² areindependently selected from the group consisting of H, substitutedalkyl, unsubstituted alkyl, substituted heteroalkyl, unsubstitutedheteroalkyl, substituted aryl, unsubstituted aryl, substitutedheteroaryl, unsubstituted heteroaryl, substituted heterocycloalkyl,unsubstituted heterocycloalkyl; and a is an integer of 0, 1, 2, 3, or 4.3. The compound of claim 2, wherein m is not 0 and-(AA¹)_(c)-(L²)—C(O)-(L¹)_(m)- comprises the structure:

wherein each R²⁴ is a member independently selected from the groupconsisting of H, substituted alkyl, unsubstituted alkyl, substitutedheteroalkyl, and unsubstituted heteroalkyl.
 4. The compound of claim 2,having the structure:

wherein Z is a member selected from O, S and NR²³, wherein R²³ is amember selected from H, substituted and unsubstituted alkyl, substitutedand unsubstituted heteroalkyl, and acyl; and wherein X¹ is a halogen. 5.The compound of claim 1, which is selected from the group consisting of:

wherein X¹ is Cl or Br, and Ab is an antibody, or fragment thereof. 6.The compound of claim 1, wherein L⁴ comprises a polyethylene glycolmoiety.
 7. The compound of claim 6, wherein the polyethylene glycolmoiety contains 2-6 repeat units.
 8. The compound of claim 1, wherein(AA¹)_(c) is a peptide sequence cleavable by a protease expressed intumor tissue.
 9. The compound of claim 1, wherein (AA¹), is a peptidesequence selected from the group consisting of Val-Cit, Val-Lys,Phe-Lys, Lys-Lys, Ala-Lys, Phe-Cit, Leu-Cit, Ile-Cit, Trp, Cit, Phe-Ala,Phe-N⁹-tosyl-Arg, Phe-N⁹-nitro-Arg, Phe-Phe-Lys, D-Phe-Phe-Lys,Gly-Phe-Lys, Leu-Ala-Leu, Ile-Ala-Leu, Val-Ala-Val, Ala-Leu-Ala-Leu (SEQID NO: 1), β-Ala-Leu-Ala-Leu (SEQ ID NO: 2) and Gly-Phe-Leu-Gly (SEQ IDNO: 3).
 10. The compound of claim 1, wherein (AA¹)_(c) is Val-Cit orVal-Lys.
 11. The compound of claim 1, wherein D has the structure:

wherein Z is a member selected from O, S and NR²³ wherein R²³ is amember selected from H, substituted and unsubstituted alkyl, substitutedand unsubstituted heteroalkyl, and acyl; R¹ is H, substituted orunsubstituted lower alkyl, C(O)R⁸, or CO₂R⁸, wherein R⁸ is a memberselected from group consisting of substituted alkyl, unsubstitutedalkyl, NR⁹R¹⁰, NR⁹NHR¹⁰, and OR⁹ in which R⁹ and R¹⁰ are membersindependently selected from H, substituted and unsubstituted alkyl, andsubstituted and unsubstituted heteroalkyl; and R² is H, substitutedalkyl or unsubstituted lower alkyl.
 12. The compound of claim 1, whereinD has the structure:

wherein Z is a member selected from O, S and NR²³ wherein R²³ is amember selected from H, substituted or unsubstituted alkyl, substitutedor unsubstituted heteroalkyl, and acyl; R¹ is H, substituted orunsubstituted lower alkyl, C(O)R⁸, or CO₂R⁸, wherein R⁸ is a memberselected from NR⁹R¹⁰ and OR⁹, in which R⁹ and R¹⁰ are membersindependently selected from H, substituted or unsubstituted alkyl andsubstituted or unsubstituted heteroalkyl; R^(1′) is H, substituted orunsubstituted lower alkyl, or C(O)R⁸, wherein R⁸ is a member selectedfrom NR⁹R¹⁰ and OR⁹, in which R⁹ and R¹⁰ are members independentlyselected from H, substituted or unsubstituted alkyl and substituted orunsubstituted heteroalkyl; R² is H, or substituted or unsubstitutedlower alkyl or unsubstituted heteroalkyl or cyano or alkoxy; and R^(2′)is H, or substituted or unsubstituted lower alkyl or unsubstitutedheteroalkyl.
 13. A pharmaceutical formulation comprising a compoundaccording to claim 1 and a pharmaceutically acceptable carrier.